Vehicle information system

ABSTRACT

A vehicle information system which includes an in-vehicle system  105  and a centralized server system  120 . The in-vehicle system communicates with the server system using a wireless communication link  110 , such as over a cellular telephone system. A position system, such as a set of GPS satellites  140 , provides positioning signals that are used by the in-vehicle systems, and optionally by the centralized server system to increase the accuracy of position estimates. In one version of the system, an operator specifies a destination to an in-vehicle system which validates the destination. The in-vehicle system transmits specification of the destination to a server system  125  at the centralized server. The server system computes a route to the destination and transmits the computed route to the in-vehicle system. The in-vehicle system guides the operator along the route. If the in-vehicle system detects that the vehicle has deviated from the planned route, it replans a new route to the destination using an in-vehicle map database.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/056,150, filed Aug. 19, 1997.

BACKGROUND

[0002] This invention relates to an information system for motorvehicles.

[0003] Vehicle information systems have been developed that providevarious types of information to operators of those vehicles. Inparticular, navigation systems have been developed. One type ofnavigation system, an autonomous navigation system, uses an on-boardmap, typically stored on a removable medium such as a compact opticaldisk (e.g., CD-ROM). The navigation system uses the on-board map to plana route from a starting point to a destination, which is specified bythe operator of the vehicle. Updating an autonomous system's map, forexample to add or correct information, typically involves replacing theremovable medium.

[0004] In some navigation systems the operator inputs the desireddestination (and the current location, if required by the system) byentering a spelling of the destination. Some systems also allow anoperator to select from a stored list of “points of interest,” such as alist of gas stations or restaurants. Once the operator inputs thedestination, the system plans a route along the road network to thedestination. The route is typically planned to provide a shortestdistance or to try to provide the shortest travel time. Once the routeis planned, the operator is guided by the system along the route.

[0005] Various approaches to route guidance have been used. Aparticularly simple approach is to provide the operator with a sequenceof discrete instructions, for instance, at intersections where theoperator must turn from one street onto another. The operator indicateswhen he or she is ready for the next instruction. For example, theinstructions are provided as an audio output, and the operator says“next” when ready for another instruction.

[0006] Another approach to route guidance uses a displayed map on whichthe planned route and the vehicle's location are dynamically displayed.The operator uses the map to decide when and where to turn in order tofollow the planned route.

[0007] Some guidance approaches are aided by in-vehicle sensors that areused to estimate the location of the vehicle. For instance, a magneticcompass is used to estimate the direction of travel, and a velocitysensor is used to estimate the distance traveled. In addition, thelocation of the vehicle can be estimated using the Global PositioningSystem (GPS). In GPS, multiple satellites emit signals that allow anin-vehicle GPS receiver to estimate its absolute location.

[0008] Other types of vehicle information systems have also beendeveloped. In some systems, traffic related information, such as trafficadvisories, is broadcast to specially equipped in-vehicle radioreceivers.

SUMMARY

[0009] In general, in one aspect, the invention is a vehicle informationsystem. The vehicle information system features an in-vehicle system anda centralized server system. The in-vehicle system communicates with theserver system using a wireless communication link.

[0010] In general, in another aspect, the invention is a method forguiding a vehicle through a road network from a starting location to adestination. The method features transmitting a specification of thedestination to a server, for example by transmitting a street address oran identifier of a point of interest. The server determines a route tothe specified destination and transmits a specification of the route tothe vehicle. The method also includes receiving from the server aspecification of a planned route through the road network to thedestination as well as receiving from the server a map that includes aspecification of the road network in the vicinity of the planned route.For instance, the map can correspond to one or more regions aroundparticular points on the planned route, correspond to a “corridor”around the planned route, or be a complex shaped region in the vicinityof the route. The planned route can include specifications of a multiplemaneuvers to be carried out by the vehicle, and the specification ofeach maneuver then includes a location of the maneuver. The map can bein the vicinity of the starting location, or in the vicinity of one ofthe specified maneuvers. The method can also feature tracking thelocation of the vehicle. The method can also feature displaying thereceived map in conjunction with a representation of the planned route,and a location of the vehicle.

[0011] An advantage of the invention is that the vehicle does not haveto have a prestored map to plan a route to a destination. Also, theinvention provides a way of displaying a map of the vicinity of thestarting point or of intermediate maneuver points of a planned routewithout requiring that the map be prestored in the vehicle. Thedisplayed map can provide useful information to an operator of a vehicleduring difficult maneuvers where turn-by-turn instructions.

[0012] In general, in another aspect, the invention is a method fortracking a vehicle. The method features receiving a reference signalfrom a positioning system, for example receiving signals from GPSsatellites, and computing position data related to the location of thevehicle using the received reference signal. For example, the positiondata can be latitude and longitude estimates, or can be GPS pseudorangemeasurements. The method also features transmitting the position data toa server and receiving from the server position correction data. Forexample, the position correction can be a deviation in latitude andlongitude, or can be correction terms to be applied to GPS pseudorangemeasurements. The method also features determining estimated coordinatesof the vehicle including combining data computed from the receivedreference signal and the position correction data.

[0013] The method can feature repeatedly computing the position data,and determining the estimated coordinates, including combining theposition data and the position correction data. The method can alsofeature, subsequent to the interval of time, repeatedly computing theposition data and determining estimated coordinates of the vehicle usingthe position data without using the correction data.

[0014] In general, in another aspect, the invention is a method fortracking a vehicle. The method features receiving a specification of afirst location which includes coordinates, such as latitude andlongitude, of the first location. The method includes determining whenthe vehicle is at or passes near the first location. The method includescomputing first position data using a reference signal received from apositioning system at the time at which the vehicle was determined to beat the first location. For instance, the positioning system can be a GPSpositioning system, and the computed first position data can includepseudorange measurements derived from GPS satellite signals receivedwhen the vehicle was at or near the first location. The method furtherincludes computing position correction data using the first positiondata and the coordinates of the first location. For instance, computingthe position correction data can include computing pseudorangecorrection data based on the latitude and longitude of the firstlocation and on the pseudorange measurements derived from GPS satellitesignals received when the vehicle was at or near the first location. Themethod further includes computing second position data using a referencesignal received from the positioning system at a second time subsequentto the time at which that the vehicle was determined to be at the firstlocation, and then determining coordinates of the vehicle at the secondtime including combining the correction data and the second positiondata.

[0015] The method can feature including in the specification of thefirst location a specification of a maneuver to be carried out by thevehicle at the first location. Determining when the vehicle is at thefirst location then includes detecting when the vehicle performs thespecified maneuver, for instance using vehicle sensors such as acompass, accelerometers, or a gyroscope.

[0016] In general, in another aspect, the invention is a method fordetecting when a vehicle deviates from a planned route. The methodfeatures tracking a first estimated position of the vehicle usingsignals from a positioning system that are received at the vehicle, forexample, using a GPS positioning system. The method also featurestracking a second estimated position of the vehicle using an estimate ofthe distance traveled along the planned route. The vehicle is detectedto has deviated from the planned route when the first estimated positionand the second estimated position differ by at least a tolerancedistance.

[0017] The method can feature detecting when the vehicle is at a firstpoint on the planned route, such as a maneuver point, and estimating thedistance traveled along the path following the first point.

[0018] The method can also feature adjusting the tolerance distance,including reducing the tolerance distance when the vehicle is detectedto be at the first point on the planned route, and increasing thetolerance distance as the vehicle travels along the path following thefirst point.

[0019] In general, in another aspect, the invention is a method forproviding guidance instructions to a vehicle operator following aplanned route that includes a sequence of maneuver points. The methodincludes detecting when the vehicle is at a first maneuver point, andtracking the distance traveled by the vehicle from the first maneuverpoint along the planned route. When the tracked distance is within apredetermined notification distance of the distance between the firstmaneuver point and a subsequent maneuver point along the planned routethe operator is notified of the subsequent maneuver.

[0020] In general, in another aspect, the invention is a method forspecifying a location in a vehicle navigation system. The methodfeatures providing an in-vehicle map database to an in-vehicle system.The in-vehicle database includes data related to valid locationspecifications for accessing a server map database at a server system.The method also features accepting a location specification, forinstance, for an operator using a user interface in the vehicle. Thesystem validates the location specification using the in-vehicle mapdatabase and then transmits the validated location specification to theserver system.

[0021] The method can also feature providing the server map database tothe server system and accessing the server map database using thereceived validated location specification. In addition the method canalso include determining a route to the specified location using theserver map database, and transmitting the determined route to thein-vehicle system.

[0022] In general, in another aspect, the invention is method forestimating a location of a vehicle. The method includes determining aseries of vehicle position estimates using a positioning system, andrecording each of the vehicle position estimates in the series. Forexample, the position estimates are recorded in a non-volatile memory asthe vehicle reaches a destination. The method further includesestimating the location of the vehicle including retrieving the mostrecently recorded in the series of location estimates, for instanceafter the vehicle is started after a period of being parked at thedestination.

[0023] The invention has the advantage that a location estimate may beobtained, even if a positioning system, such as a GPS satellite system,is out of range, or prior to the positioning system being initialized.

[0024] In general, in another aspect, the invention is a method forvehicle guidance. The method features receiving at the vehicle a plannedroute to a destination location from a server, and storing the plannedroute at the vehicle. The method also includes providing instructions toan operator of the vehicle according to the stored planned route, forexample, providing instructions at each of a series of maneuvers alongthe route. The method includes tracking a location of the vehicle anddetecting whether the vehicle has deviated from the planned route. Ifthe vehicle is detected to have deviated from the planned route, themethod then includes planning a new route to the destination location.Planning the new route does not necessarily require furthercommunication with the server. Planning the new route can includedetermining the location of the vehicle and accessing a map databasestored in the vehicle.

[0025] The method can also include establishing a wireless communicationchannel with the server, transmitting a specification of the destinationlocation over the wireless communication channel, and then terminatingthe wireless communication channel after receiving the planned route.

[0026] Advantages of this method include providing a server based routeplanning service to a vehicle, without requiring ongoing communicationwith the server to carry out guidance and route replanning functions.

[0027] In general, in another aspect, the invention is a method forcollecting traffic information. The method includes tracking thelocation of a vehicle, including detecting when the vehicle traverseseach of a plurality of segments of a road network. For each detectedsegment, the method includes logging traffic-related data, includinglogging data related to the vehicle's speed on the detected segment. Themethod then includes transmitting the logged data to a server The methodcan feature receiving a command from the server to enable logging of thetraffic-related data at a vehicle. The method can also feature receivingat a vehicle a request to transmit the logged data to the server.

[0028] In general, in another aspect, the invention is a method forcollecting traffic information. The method includes tracking thelocation of a vehicle, including detecting when the vehicle traverseseach of a set of segments of a road network. For each detected segment,the method features comparing the vehicle's speed on the segment to astored speed for that segment, and if the vehicle's speed on the segmentdeviates from the stored speed, transmitting a traffic notificationidentifying that segment to a server.

[0029] In general, in another aspect, the invention is a method forcollecting traffic information. The method includes receiving trafficrelated data from a set of vehicles and updating a traffic databaseusing the received traffic related data. Updating the database includesupdating speed information associated with multiple road segments in aroad network. The method also features planning a route through the roadnetwork from a starting to a destination location using the speedinformation associated with the road segments.

[0030] The method can also feature enabling a subset of an available setof probe vehicles to provide the traffic related data, and can, inaddition, feature determining a part of the traffic database to targetfor updating, for instance, according to a the part of the databasecorresponding to a geographic area. Enabling the subset of probevehicles then includes enabling probe vehicles according to the part ofthe database that is targeted.

[0031] In general, in another aspect, the invention is a method forspecifying a destination to a vehicle navigation system. The methodincludes accessing a list of categories of destinations, and accepting aselection from the list of categories, for example, from an operatormaking the selection on a in-vehicle user interface. The method includestransmitting the selection from the list of categories to a serversystem, and subsequently receiving a list of destinations from theselected category from the server system. The method then includesaccepting a selection from the list of destinations and transmitting theselected destination to the server system.

[0032] The method can also feature transmitting data related to thelocation of the vehicle to the server system. The received list ofdestinations then includes destinations that are in the vicinity of thevehicle.

[0033] In general, in another aspect, the invention is a method forconfiguring a vehicle navigation system. The method includes providing aserver map database to a server. The server map database includes datarelated to a plurality of road segments in a road network. The methodalso includes providing a vehicle map database to an in-vehicle system.The vehicle map database includes data related to a subset of theplurality of road segments in the server map database which satisfy acommon criterion, for instance related to the road class of the roadsegments.

[0034] In general, in another aspect, the invention is an in-vehicle mapdatabase. The database includes a first stored table and a second storedtable. The first stored table includes multiple records each including afield containing a reference to a record containing a base name of astreet in the second stored table, and a second field which identifies aprefix, a suffix, or a street type. The second stored table includesmultiple records, each including a base name of a street stored in acompressed format.

[0035] In general, in another aspect, the invention is method fortransmitting a route to a vehicle navigation system. The route includesmultiple intermediate points joined by road segments. The methodincludes transmitting a specification of the location of a first of theintermediate points, and transmitting a specification of a differencebetween the location of a second of the intermediate points and thefirst of the intermediate points. The specification of the differencecan use fewer than an allocated number of bits.

[0036] The method can also feature planning an initial route. Theinitial route includes an initial set of multiple intermediate pointscoupled by road segments. The planned route is formed from the initialroute. For any of the road segments in the initial route for which thedifference in locations of the intermediate points bounding that segmentis greater than can be specified in the allocated number of bits, themethod includes inserting additional intermediate points on that roadsegment so that the differences between the locations of the adjacentintermediate points can each be specified in the allocated number ofbits.

[0037] In general, in another aspect, the invention is a vehiclenavigation system. The system includes an onboard computer, includingstorage for a map database, a wireless communication system for passingdata between the onboard computer and a remote server, an input/outputdevice for providing a user interface between the onboard computer andan operator of the vehicle, and a vehicle sensor for providingmotion-related signals to the onboard computer. The onboard computer isprogrammed to perform the functions of accepting a planned route fromthe server over the wireless communication system, maintaining a firstlocation estimate of the vehicle using the motion-related signals fromthe vehicle sensor, and, using the planned route and the first locationestimate, providing guidance instructions to the operator through theinput/output device.

[0038] In general, in another aspect, the invention is a method forupdating an in-vehicle navigation system. The method includes receivinga version number associated with information stored in the in-vehiclesystem. If the information stored in the in-vehicle system has a versionnumber prior to the version of information a server, the method includestransmitting update information from the server to the in-vehiclesystem. The information stored in the in-vehicle system can include mapdata or computer instructions.

[0039] The method can feature prioritizing the update information, forinstance, according to the geographic area represented by the updateinformation and transmitting the update information in order of thepriority.

[0040] In general, in another aspect, the invention is a vehicleinformation server system. The system includes a vehicle communicationinterface for providing wireless data communication between multiplevehicles and a set of information system. The set of information systemsincludes a navigation system for accepting route planning request fromthe vehicles and providing planned routes through the communicationinterface, and a communication system coupled to an external informationsystem for delivering information from the external information systemto the vehicles.

[0041] In general, in another aspect, the invention is a method forproviding traffic related information to a user. The method featuresaccepting from the user a specification of a path made up of one or moreroad segments in a road network and receiving traffic data related toroad segments in the road network. If the received traffic dataindicates an exceptional traffic condition on the specified path, theuser is notified of the traffic condition.

[0042] Other features and advantages of the invention will be apparentfrom the following description, and from the claims.

DESCRIPTION OF DRAWINGS

[0043]FIG. 1 is a block diagram of a vehicle navigation system;

[0044]FIG. 2 is a block diagram of in-vehicle components of the system;

[0045] FIGS. 2A-C show an integrated input/output device;

[0046]FIG. 3 is a block diagram including components of a server system;

[0047] FIGS. 4A-B show an in-vehicle system software architecture;

[0048]FIG. 5 is a block diagram of a server system softwarearchitecture;

[0049]FIG. 6 is a schematic map showing the road network in an exemplaryregion;

[0050]FIG. 7 is a graph representation of the road network in theexemplary region;

[0051]FIG. 8 illustrates an exemplary planned route that is downloadedfrom a server system to a vehicle;

[0052]FIG. 9 is an exemplary spot map that is downloaded from a serversystem to a vehicle;

[0053]FIG. 10 is a main roads map that is preloaded in a vehicle;

[0054]FIG. 11 shows data structures of an in-vehicle database;

[0055]FIG. 12 shows the structure of text tables in the in-vehicledatabase;

[0056]FIG. 13A shows a representative link of a main roads network;

[0057]FIG. 13B shows data structures of an in-vehicle database encodinga main roads network;

[0058]FIG. 14 shows elements of an in-vehicle database which encodePoints of Interest information;

[0059]FIG. 15A is a pseudocode listing of an in-vehicle route planningprocedure;

[0060]FIG. 15B is a pseudocode listing of a server route planningprocedure;

[0061]FIG. 16 is a pseudocode listing of a startup maneuver procedure;

[0062]FIG. 17 is a pseudocode listing of a route following procedure;

[0063]FIG. 18 is a pseudocode listing of a route replanning procedure;

[0064]FIG. 19 illustrates a extensible server architecture;

[0065] FIGS. 20A-20C illustrate approaches to updating an in-vehiclesystem;

[0066] FIGS. 21A-21B illustrate additional information services providedby a server system; and

[0067]FIG. 22 is a block diagram of an extensible server system.

DESCRIPTION

[0068] 1 Overview (FIGS. 1, 6-10)

[0069] 1.1 Architecture (FIG. 1)

[0070] Referring to FIG. 1, a vehicle information system providesservices, including a route planning and guidance (i.e., a “navigation”)service, to the operators of multiple vehicles 100, which are free todrive throughout a wide geographic area. To provide these services tothe operators of the vehicles, the vehicle information system performssome functions in a server system 125 at a centralized server 120 thatis at a fixed location, and other functions in in-vehicle systems 105installed in each of the vehicles 100. The vehicle information systemalso includes a positioning system that provides a reference forestimating the locations of vehicles 100 in absolute terms (i.e., interms of their latitudes and longitudes). In particular, GlobalPositioning System (GPS) satellites 140 provide signals that whenreceived at the vehicles enable the in-vehicle systems to estimate theirlocations.

[0071] The navigation service of the vehicle information system as awhole, which are provided through a combination of functions that areperformed by server system 125 and by an in-vehicle system 105, enablean operator of a vehicle to specify a desired destination, and then tobe guided by the system to that destination while driving the vehicle.In-vehicle system 105 tracks (i.e., repeatedly estimates) the positionof the vehicle as it travels to the desired destination, and providesinstructions to the operator to guide the operator to the desireddestination. For instance, in-vehicle system 105 provides an instructionto make a turn at an upcoming intersection while the vehicle isapproaching the intersection. Also, in-vehicle system 105 typicallydetermines when the operator has made an error and the vehicle is off aplanned route. If the vehicle is off route, in-vehicle system 105provides the operator with instructions to continue to guide the vehicleto the destination despite the error.

[0072] Server system 125 provides various services to in-vehicle system105, in a “client-server” arrangement in which in-vehicle systems 105request services from server system 125. For instance, a route planningfunction is performed by server system 125 at the request of in-vehiclesystem 105 while route guidance functions are performed by in-vehiclesystem 105.

[0073] In-vehicle systems 105 are coupled to server system 125 bywireless communication links. In particular, in-vehicle systems 105 attimes communicate with server system 125 over signal paths 110 usingmodulated data signals that are passed over a standard analog cellulartelephone system (i.e., using the Advanced Mobile Phone Service (AMPS)standard). An in-vehicle system 105 typically operates in an autonomousmode after an initial exchange with server system 125. During theinitial exchange, a starting location (or other location-related data),speed and heading, and a desired destination are uploaded from thein-vehicle system to the server system and then a planned route isdownloaded from the server system to the in-vehicle system. Afterplanned route information is downloaded to the vehicle from the serversystem, the in-vehicle system does not require further interaction withthe server system to operate in its autonomous route guidance mode.While in the autonomous route guidance mode the in-vehicle system canrecover from an operator going off the planned route without necessarilyrequiring further communication with the server system.

[0074] In-vehicle systems 105 receive signals from GPS satellites 140over radio frequency communication paths 112. Server system 125 alsoreceives signals from GPS satellites 140 over radio frequencycommunication path 122. As is described more fully below (see Section2.4), data derived from signals received by server system 125 from GPSsatellites 140 is used at times by both server system 125 and in-vehiclesystems 105 to improve the location estimates of vehicles 100, forinstance, using “differential” GPS calculations.

[0075] Referring still to FIG. 1, server system 125 relies on a mapprovider 160, for instance, a vendor of map-related information, toprovide information related to the road network, including the locationsand types of road segments that interconnect to form the road network.Map provider 160, or some other external information provider, alsoprovides other map-related information such as the locations of typicalpoints of interest such as city centers, restaurants, and gas stations.

[0076] In some versions of the system, server system 125 also serves asa gateway to external information systems 130. These external systemsprovide information used by server system 125, or provide informationthat is passed directly to in-vehicle systems 105. For instance, anexternal information system 130 can provide traffic-related informationthat is used by server system 125 to determine a fastest route from astarting to a destination location. In another instance, an externalinformation system 130 can provide communication services to vehicleoperators, such as a paging service.

[0077] Alternative communication approaches between in-vehicle systems105 and server system 125 can be used. Use of standard analog cellulartelephone links is useful due to the broad geographic coverage in NorthAmerica of the infrastructure needed to support such links. In otherparts of the world, digital cellular telephone links may be moreappropriate if the necessary infrastructure is available. Such adigital-based infrastructure is expected to be available in NorthAmerica in the future. A satellite-based communication system canalternatively be used to link the in-vehicle systems to the serversystem. Also, other wireless data communication systems can beequivalently used to couple in-vehicle systems 105 and server system125. Such systems are currently being deployed in North America (e.g.,ARDIS, RAM, CDPD, GSM), although the geographic coverage is not yetadequate to support this system and provide broad geographicavailability to vehicle operators. Many wireless communication systemsalso include a “short message” capability with which short messages canbe transferred. Such short message services can alternatively be usedfor some types of communication between the in-vehicle systems and theserver system, for instance for notification of exception conditions.

[0078] Also, alternative positioning systems can be used rather thanrelying on signals from GPS satellites 140. For instance, a roadsideoptical or radio frequency beacon systems can be used to providelocation information to vehicles. Such a roadside beacon system is notbroadly available in North America. On the other hand, the GPS-basedapproach provides broad geographic coverage today.

[0079] Centralized server 120 is “centralized” in that it providesservices at one location for vehicles that are distributed throughout ageographic area. The centralized server's location does not have to be“central” or even located in the same geographic area as the vehicles itservices. Also, although the system is described in terms of a singlecentralized server 120, multiple servers can alternatively be used. Whenmultiple servers are used, in-vehicle systems 105 can be configured toaccess particular servers for all, or for particular types of, servicerequests.

[0080] 1.2 Operation (FIGS. 6-10)

[0081] General operation of the navigation service of the vehicleinformation system can be understood with reference to FIGS. 6-10, whichillustrate various representations of exemplary maps and routes that areused in the system. These drawings correspond to a common geographicarea that is shown schematically in FIG. 6. The geographic area shown isonly a very small portion of the area that is typically supported by thenavigation service, which may be as large as the United States ormultiple countries in Europe.

[0082] Referring to FIG. 6, a map 600 is illustrated with three classesof roads shown in different line widths. In general, roads areclassified according to their size or typical vehicle speed, forexample, highways, limited access roads, main roads, and side streets.In FIG. 6, a highway 610 is shown as a thick line running along thevertical orientation of the drawing. A set of main roads 620, 622, 624,and 626, which is shown in medium thickness lines, form an intersectingnetwork. Main roads 620 and 622 are connected to highway 610 at twoon-ramps, 612 and 614, respectively. A set of residential roads (sidestreets) 630-636 completes the road network.

[0083] In this example, an operator and vehicle are initially at thepoint marked ‘X’ 690. The operator wants to get to a desired destination692 that is not shown in the drawings, but that is best accessed byfollowing highway 610 as indicated in the drawings.

[0084] As the first step, the operator enters a specification of desireddestination 692 into in-vehicle system 105. For instance, the operatorenters the city, street, and street number of a destination address. Thedestination is validated by the in-vehicle system, for instancevalidating that the street address is in an allowable range for thespecified street.

[0085] After in-vehicle system 105 has accepted and validated thedestination specification, it establishes a communication session withserver system 125 over cellular telephone link 110 and sends thedestination specification to the server system. The in-vehicle systemalso sends information to the server system that allows the serversystem to determine the vehicle's starting location 690. For instance,the in-vehicle system sends the estimated latitude and longitude outputobtained from a GPS receiver in the vehicle, or sends other raw outputfrom its GPS receiver.

[0086] Referring to FIG. 7, the server system includes a stored detailedrepresentation of the road network 700. The network is represented as agraph with a set of nodes, indicated in the drawing by open circles,that are interconnected by links (arcs) that correspond to roadsegments. Links in the graph have associated stored data which includesthe class of the road represented by the links. Each node in the graphhas associated data including its latitude and longitude (orequivalently its relative location to another node that is at a knownlocation), as well as other information, such as which turns from onelink to another link joined at the node are valid. Many links areapproximated by straight line segments joining the nodes at each end ofthe link. Some links, such as the links joining nodes 733 and 735 ornodes 716 and 725, represent curved road segments. To represent suchcurved road segments, links can include one or more “shape points,”represented as hatched circles 780-785 in the drawing. Each shape pointhas location data associated with it. The segments between adjacentshape points, or between nodes and adjacent shape points, areapproximated by straight line segments.

[0087] Server system 125 uses the information provided by the in-vehiclesystem related to the location of the vehicle 690 to determine thestarting latitude and longitude of the vehicle. Based on the vehicle'slatitude and longitude, speed, and heading, the server system finds thevehicle's starting link in its graph representation of road network 700.In this example, this first point on the road network is on the linkjoining nodes 753 and 763.

[0088] The server system next computes a best path to destination 692.“Best” can be based on a variety of criteria such as the smallest totaldistance, or the shortest expected travel time using information relatedto the expected speed of travel along links of the roadway graph. Inthis example, this planned route is illustrated by the dotted line 792.Referring back to FIG. 6, this planned route has the vehicle starting onresidential road 635 and first making a left on residential road 632.The vehicle then is to make a right turn onto main road 628, and a rightonto main road 620. Main road 620 merges onto highway 610. The vehiclethen is to continue along highway 610 toward destination 692.

[0089] Referring to FIG. 8, planned route 800 is downloaded from theserver system to the in-vehicle system in the form of a sequence oflinks joined by nodes. Each node along the route (other than necessarilythe start node) corresponds to a node in the server's road network 700(FIG. 7). Nodes along planned route 800 correspond to “maneuvers” thatmust be carried out by the operator. For example, the maneuver at node790 is “turn left onto road 635” (See FIG. 6). Each link along the routecan have one or more “way points.” Way points correspond to shape pointsin the server's road network 700, or to nodes which are intersections atwhich the operator does not have to make a maneuver, that is, nodes ofthe server's road network 700 at which the operator simply continueswithout turning or making some other maneuver. In FIG. 8, nodes 733,780, and 781 are way points on the link joining maneuver points 732 and735.

[0090] In principle, if the operator could always be expected to followdirections exactly, then the operator will drive to the desireddestination. However, various factors may result in the operator notreaching the desired destination without further planning. These factorsinclude:

[0091] Inaccuracy in the estimate of the vehicle's initial location, forexample due to closely spaced side streets,

[0092] The operator's inability to follow directions, particularlyduring the initial startup portion of a route where the directions maybe complicated,

[0093] Errors in the system's map of the road network, for instance, dueto unexpected road construction, and

[0094] Inaccuracy in estimating the distance traveled by the vehicle.

[0095] In order to account for errors associated with the startupportion of the route, the server system downloads to the in-vehiclesystem a detailed map 900, known as a “spot map,” around initiallocation 690. Referring to FIG. 9, map information related to nodes andlinks in the vicinity of starting location 690 are downloaded. Spot map900 has as high a level of detail as does the server's road network 700,but is limited geographically, for instance including all nodes withintwo links of the starting location.

[0096] The server system can also download a spot map around one, ormore, maneuver points, or around the destination. For instance, if amaneuver is particularly complex, the server system would download aspot map around that maneuver point.

[0097] After planned route 800 and spot map 900 are downloaded to thevehicle, communication between in-vehicle system 105 and server system125 is typically completed. At this point, the operator can preview theroute, or can start traveling to the destination. The operator can alsostart traveling before the planned route is downloaded. The in-vehiclesystem begins providing initial guidance commands and displaying thespot map around the starting location to the operator as soon as it isdownloaded without necessarily waiting for the complete route to bedownloaded.

[0098] While traveling to the destination, the in-vehicle systemattempts to track the location of the vehicle. As the in-vehicle systemdetermines that the vehicle is approaching each maneuver point, itprovides aural and graphical instructions to the operator regarding theaction to take at that maneuver point. If a spot map has been downloadedfor the maneuver, the in-vehicle system displays the spot map inaddition to, or instead of, the graphical instructions.

[0099] During the initial portion of the trip or near a maneuver forwhich the server system has provided a spot map, while the vehicle is inthe region of a spot map 900, the spot map is used by the in-vehiclesystem to guide the operator onto the planned route. In particular, thein-vehicle system displays the spot map and the initial portion of theplanned route to the operator. In addition, the in-vehicle systemdisplays the tracked location of the vehicle in conjunction with thespot map. This allows the operator to recover from errors during theinitial portion of the trip by seeing that the tracked location is notfollowing the planned route, and using the roads shown on the spot mapto determine what turns to make to get back to the planned route.

[0100] The in-vehicle system also has a preloaded main roads network1000, which is a stored version of the map that includes only main andlarger roadways (i.e., it does not include residential roads). A portionof the main roads network 1000 is shown in FIG. 10. Main roads network1000 has a similar form as the server's road network 700 shown in FIG.7, except that fewer links are included. For reference, the plannedroute 792 is illustrated by a dotted line.

[0101] While traveling toward the destination, the in-vehicle systemtracks an estimated location of the vehicle. If the operator does notproperly follow the directions, the in-vehicle system will typicallydetect when the vehicle has diverged too far from the planned route.When it detects that the vehicle is off-route, it plans a correctedroute based on the main roads map shown in FIG. 10 which get the vehicleback onto the originally planned route.

[0102] Referring back to FIG. 6, in this example, the operator fails tomake the right turn from main road 628 onto main road 620, continuinginstead on main road 628. Referring back to FIG. 10, the in-vehiclesystem determines that the vehicle is off-route at a point 1010, whichcorresponds to a point on a main road segment between nodes 732 and 722when it should have been at a point on the link joining points 732 and735. Using its main road network 1000, the in-vehicle system plans acorrected route indicated by the dashed line 1012. This re-planned routejoins the originally planned route at point 725. Note that in replanninga route after an off-route condition occurs, the in-vehicle system doesnot necessarily have to contact the server system, relying instead onits main roads network 1000.

[0103] The in-vehicle system therefore uses a combination of main roadsnetwork 1000 that is preloaded into the vehicle and spot maps 900 thatare downloaded to the vehicle along with planned route 800 to replan theroute when the vehicle is detected to not be following the plannedroute.

[0104] In an alternative version of the system, spot maps 900 can beused to augment main roads network 1000 to re-plan the route if theoperator fails to follow the planned route during the initial portion ofthe trip.

[0105] In the system operation described above, a vehicle operatorreceives instructions in the form of

[0106] Graphically presented maneuver instructions,

[0107] Aural maneuver instructions, and

[0108] Spot map based instructions.

[0109] Alternative versions of the system use subsets of these forms ofinstructions. For instance, a version of the system can use auralinstructions alone. Another version of the system can use graphicallypresented maneuver instructions without any map based or auralinstructions. Other combinations or instruction modes can be used aswell. Furthermore, alternative versions of the system can give thevehicle operator control over which instruction modes are used, forinstance, allowing the operator to switch between map based andgraphical instruction based modes.

[0110] 2 Harware and Software Architecture (FIGS. 2-5)

[0111] 2.1 In-Vehicle System Components (FIG. 2)

[0112] Referring to FIG. 2, each in-vehicle system 105 includes anonboard computer 210 which is used to coordinate the operation of othercomponents, including sensors 230, which provide information related tothe motion of the vehicle, input/output (I/O) devices 240, which providean interface between the operator of the vehicle and the navigationsystem, and communication system 250, which provides communication linksfrom GPS satellites 140 and to and from server system 125. Onboardcomputer 210 is also coupled to vehicle systems 270, which include doorlocking system 272 and airbag system 274.

[0113] Onboard computer 210 has limited storage and processingcapabilities. In this version of the in-vehicle system, onboard computer210 includes a processor 212 coupled to other components of the onboardcomputer over a data bus 214. The other components includes dynamicrandom access memory (DRAM) 220, which provides 2 MB of working storagefor processor 212, erasable programmable read-only memory (EPROM) 218,which provides 4 MB of non-volatile storage, and universal asynchronousreceiver-transmitter (UART) 216, which provides serial communicationcapabilities to other system components. Alternative hardwareconfigurations, for instance, with more or less memory, can be used.

[0114] Processor 212 is also coupled to a static storage 222 which is anon-volatile storage used to store code and data for operation of thesystem. In particular, as is described further below, static storage 222is used to store map-related information, such as main roads network1000 (FIG. 10), which is used during route planning and guidanceprocedures executed on onboard computer 210. Static storage 222 is aremovable 40 MB flash memory system which emulates a disk storagedevice. Alternative static storage devices can be used, includingremovable and non-removable disk storage devices and semiconductormemories.

[0115] Sensors 230 include a velocity sensor 232 which provides avelocity signal to onboard computer 210. The velocity signal encodes thedistance traveled by the vehicle by providing a constant number ofpulses per revolution of the output of the vehicle's transmission, andwhich therefore provides a relative constant number of pulses per miletraveled. Sensors 230 also includes a magnetic compass 234 whichprovides a signal to onboard computer 210 encoding the orientation ofthe vehicle. Alternative versions of the system do not necessarilyinclude magnetic compass 234, relying only on the velocity signal. Also,alternative versions may include other sensors of the state of thevehicle, including a gyroscope or accelerometers for determining therate of rotation of the vehicle, or a differential velocity sensor,which provides the relative speed of the wheels on either side of thevehicle thereby encoding a turning radius of the vehicle as it goesthrough a turn.

[0116] I/O devices 240 includes a display 242. In versions of thein-vehicle system in which only graphical commands are displayed,display 242 is a small (e.g., 4-5 lines of text high, 64×240 pixels)monochrome liquid crystal display (LCD) which is used to provide textand schematic image instructions to the operator of the vehicle. Inversions of the in-vehicle system in which spot maps are displayed tothe operator, display 242 is 4 to 5 inch diagonal display withapproximately 200×200 pixels, which is large enough and has a highenough resolution to provide a detailed map display to the operator thatcan be used to provide map-based directions to the operator. Also, inalternative versions of the system, visual feedback is not necessarilyused, relying instead solely on audio instructions from the system tothe operator.

[0117] I/O devices 240 also includes an input device 244. Input device244 includes multiple push buttons associated with display 242. Theoperator uses these buttons to select alternatives shown on display 242,or to scroll the list of displayed alternatives. Alternative versions ofthe system can include an alphanumeric keyboard coupled to the onboardcomputer.

[0118] Referring to FIGS. 2A-C, an integrated I/O device 241 includesdisplay 242 and a set of four rocker switches that are part of inputdevice 244. One rocker switch is dedicated to “menu” and “cancel” inputswhile the other three are reconfigurable. Referring to FIG. 2A, display242 is at times used to display both text commands and graphicalrepresentations of commands. Referring to FIGS. 2B-C, display 242 isused at times to provide visual feedback to the operator when inputtinginformation. FIG. 2B illustrates selection from a list and FIG. 2Cillustrates spelled input in which the operator uses the rotary switchto select letters to spell an input word.

[0119] Referring back to FIG. 2, I/O devices 240 also include a voiceoutput device 246. Voice output device 246 provides audio output ofspeech commands that are stored or formed on onboard computer, forexample, using compressed or concatenated waveforms or a speechsynthesizer.

[0120] I/O devices 240 can be dedicated to onboard computer 210, or canalternatively be part of another vehicle component such as a radio. Inthe latter case, display 242 and input device 244 are the display andinput buttons of the other component, respectively. Many audiocomponents include standard control interfaces, such as the ACP (AudioControl Protocol) interface used in vehicles manufactured by the FordMotor Company. In such a case, onboard computer 210 can communicate withthe audio component using a standard communication interface. Voiceoutput can be provided to the operator by passing it through the audiosystem, or alternatively, onboard computer 210 can mute or attenuate theaudio system while voice output is provided through a dedicated audiopath.

[0121] Referring still to FIG. 2, communication system 250 includes aGPS receiver 252 coupled to a GPS antenna 253 for receiving signals fromGPS satellites 140. GPS receiver 252 repeatedly provideslocation-related information to onboard computer 210, for example, atone-second intervals. The location related information can be anestimated location, in terms of latitude and longitude, or other rawmeasurements that can be used to compute an estimated location. GPSreceiver 252 can also receive correction data from onboard computer 210,which it uses to compute increased accuracy location estimates from itsraw measurements. As is described further below, the correction data canbe provided by server system 125 and is used at times to increase theaccuracy of the location information provided by GPS receiver 252.

[0122] Communication system 250 also includes a cellular transceiver 254coupled to a cellular telephone antenna 255. Cellular transceiver 254provides voice and data communication capabilities to the vehicle. Amodem 256 is coupled between onboard computer 210 and cellulartransceiver 254. Data sent to and received from server system 125 over acellular telephone line passes through modem 256. Cellular transceiver254 is also coupled to a handset 260. The operator can place standardtelephone calls using handset 260 when cellular transceiver 254 is notbeing used to communicate with server system 125.

[0123] 2.2 Server System Components (FIG. 3)

[0124] Referring to FIG. 3, server system 125 includes a server computer310, which communicates with in-vehicle systems 105. Server system 125includes a telephone interface 320 for receiving and placing telephonecalls to establish data communication sessions with individualin-vehicle systems 105.

[0125] An in-vehicle system 105 initiates a communication session withserver system 125 by placing a cellular telephone call to a telephonenumber associated with the server system. The call is routed through acellular telephone network 350 to public switched telephone network(PSTN) 340 and then to telephone interface 320. Telephone interface 320answers the call. Telephone interface includes a modem function which isused to establish a data connection with modem 256 (FIG. 2) in thecalling vehicle. In alternative versions of the system, telephoneinterface 320 may be coupled directly to cellular telephone network 350.Also, the data signal may be demodulated prior to reaching the serversystem, for example, in the telephone network itself.

[0126] The server system can similarly establish a data communicationsession with a particular vehicle by placing a telephone call to thetelephone number associated with that vehicle. Cellular transceiver 254FIG. 2) determines whether the inbound call is a data call from theserver system or a voice call intended for voice communication with theoperator of the vehicle. A data call is connected to modem 256 (FIG. 2)providing a data connection between telephone interface 320 and modem256.

[0127] Server system 125 also includes a GPS receiver 325. GPS receiver325 receives signals from GPS satellites 140. Server system 125, whichis at the known location of centralized server 120, does not rely on GPSreceiver 325 to determine its location. Rather, server computer 310provides its known location (i.e., latitude and longitude) to GPSreceiver 325. Using the satellite signals and the known location of theserver, GPS receiver 325 provides in return GPS correction data, forinstance, “differential” pseudorange correction data provided accordingto the Radio Technical Commission for Maritime Services (RTCM) standardRTCM SC-104. This correction data is used to improve the locationsestimates of vehicles 100, as is described more fully in Section 2.4.

[0128] Server computer 310 includes a processor 312, working memory 314,and static storage 316. Static memory 316 includes storage formap-related information that is used by the server system in computingroutes.

[0129] Server computer is coupled to external information systems 130.For instance, external information systems can be other computerscoupled to server system 125 over a data network 330, such as theInternet.

[0130] Server system 125 receives map information from map provider 160on a removable computer medium 360, such as a optical disk (e.g.,CD-ROM). Server computer 310 reads this map data and stores a processedform of the map information in static memory 316 for further use.Alternatively, map provider 160 can provide the map information to theserver system in some other way, for example by passing it to the serversystem over data network 330.

[0131] 2.3 Map Database

[0132] The in-vehicle and server systems make use of data derived frommap information furnished by map provider 160 on computer medium 360(FIG. 3). The raw map information furnished by map provider 160 includesvarious types of information related to the road network for aparticular geographic region, such as a portion of the United States.Within this region, the information includes a representation of theroad network as a graph as illustrated in FIG. 7. Links in the graphcorrespond to segments of the road network, for example, a segment of astreet between two intersections. Nodes in the graph correspond tointersections or other points at which two or more links join. Nodesthat couple only two links are used, for example, as “shape points” whena single roadway makes a turn. This allows roadway to be wellapproximated by sequences of straight segments.

[0133] The map information includes the locations of nodes in the graph,in terms equivalent to their latitude and longitude. The map informationalso includes link information, including associations of street namesand links, and ranges of street numbers on links. Links are alsocategorized according to their size ranging from small residentialstreets to interstate highways.

[0134] An example of a map provider for this system is NavigationalTechnologies Inc. (NavTech) of Rosemont, Ill. The map information isprovided in one of a number of interchange formats, such as in theGeographic Data File (GDF) format, an international standard format. Amap in GDF format includes a data structure which associates links andnodes and their attributes, and relationships between nodes and links inthe graph. NavTech provides maps in which road links are categorized byclasses from 0 to 4, with 0 for residential (side) streets, 1 for mainstreets, 2 for arterial roads, 3 for freeways, and 4 for interstatehighways.

[0135] In alternative versions of the system, other forms of mapinformation that can be converted to a link and node representation of aroad network can alternatively be used.

[0136] 2.4 GPS and DGPS Correction

[0137] As outlined above, both the in-vehicle and server systems includeGPS receivers. GPS positioning uses the ranges to multiple satellitesthat are in precisely known orbits around the earth. A constellation ofapproximately 24 satellites is in such known earth orbits. A receiver atany point on or near the surface of the earth is typically in range of asubset of three or more of the satellites. A GPS receiver determines anestimate of its distance or range (a pseudorange measurement) to each ofthe subset of in-range satellites. It then computes itsthree-dimensional coordinates with reference to the known coordinates ofeach of the subset of satellites to which it determined pseudorangemeasurements. Based on straightforward geometric consideration (i.e.,intersections of spheres) four pseudorange measurements are sufficientto uniquely determine the coordinates of the receiver. Threemeasurements are sufficient to determine that the receiver is at one oftwo possible points, and typically, only one of the points is reasonable(e.g., it is on the surface of the earth rather than in outer space).Using three pseudorange measurements, a GPS receiver can determine atwo-dimensional location on the surface of the earth with an accuracy ofapproximately 100 meters.

[0138] The pseudorange measurements are not, however, completelyaccurate measurements of the distance from the receiver to thesatellites due to several factors. First, signal propagation speed froma satellite to a GPS receiver can vary due to variations in atmosphericconditions. Also, the transmitted signals are intentionally manipulatedby introducing varying time delay at the transmitter in order to limitthe accuracy of location estimates based solely on the pseudorangemeasurements at the receiver.

[0139] As a method of overcoming the inaccuracies in the pseudorangemeasurements, differential GPS (DGPS) is used. Differential GPS is basedon receiving signals from GPS satellites at a receiver that is at aknown location. The difference between a pseudorange measurement from asatellite to that receiver and a computed distance between the locationof the satellite and the location of the receiver is a pseudorangecorrection term for that satellite. Separate pseudorange correctionterms are computed for each satellite. To the extent that propagation isslowly varying and the intentionally introduced delays are also slowlyvarying, a pseudorange correction term for a satellite can be used tocorrect further pseudorange measurements from that satellite for a shortperiod of time relative to the rates of variation, for example for oneminute. Also, to the extent that variations in propagation speed are notgeographically local, a pseudorange correction term can be applied at aGPS receiver that is at a different location than the GPS receiver atwhich the correction term was computed.

[0140] In the vehicle information system, three approaches todifferential GPS correction are used. A first approach is generallyknown as “inverted DGPS.” In this approach, an in-vehicle system sendsthe pseudorange measurements, or other raw GPS data that is related tothe pseudorange measurements, that it obtains from its GPS receiver tothe server system over the cellular telephone link. The server systemapplies the differential correction terms it previously obtained fromits own GPS receiver to the received pseudorange measurements itreceives from the in-vehicle system and the server system calculates acorrected location for the vehicle.

[0141] In a second approach to GPS location estimation, the serversystem transmits pseudorange correction data to an in-vehicle system.The in-vehicle system provides the received correction data to its GPSreceiver which then outputs improved location estimates based on its rawpseudorange measurements and the pseudorange correction data.

[0142] A third way that differential GPS is used in the system is for anin-vehicle system to determine its own pseudorange correction data basedon its own location estimate. For instance, when an in-vehicle systemdetects that the vehicle is at a known maneuver point along a plannedroute, it computes the pseudorange correction data based on thedownloaded location of the maneuver point. The differential correctiondata is then used for a period of time after the maneuver point ispassed.

[0143] An alternative mode of correction of GPS location estimatescomputed by the in-vehicle system uses correction data in terms ofdifferences in latitude and longitude rather than differences inpseudorange measurements. For instance, the server system can provideGPS correction data that includes an offset in latitude and in longitudethat the in-vehicle system adds to the latitude and longitude locationestimates output from its GPS receiver. If this type of GPS correctionis used, the in-vehicle GPS receiver does not have to have adifferential GPS capability since the location correction is performedon the output of the GPS receiver, rather than as part of the process ofcomputing a location estimate in the GPS receiver.

[0144] 2.5 In-Vehicle Software Components (FIGS. 4A-B)

[0145] Referring to FIGS. 4A-B, software components of in-vehicle system105 which execute on onboard computer 210 (FIG. 2) include relativelystatic data stored in static storage 222, and code stored in workingstorage 410, which is made up of some combination of DRAM 220 and EPROM218 shown in FIG. 2.

[0146] Static data includes in-vehicle database 432 and software 436.Code in working storage 410 includes a navigation application 412, acommunication interface 414, and a vehicle interface 416. Communicationinterface 414 provides an interface between navigation application 412and GPS receiver 252 and cellular transceiver 254. Vehicle interface 416provides an interface between navigation application 412 and sensors230, vehicle systems 270, and I/O devices 240.

[0147] 2.5.1 In-Vehicle Database 432 (FIGS. 11-14)

[0148] In-vehicle database 432 is used by in-vehicle system 105 for twoprinciple functions. First, in-vehicle system 105 uses in-vehicledatabase 432 in the destination specification phase in which thedatabase is used to determine alternatives to present to the operator,and to validate inputs from the operator. Second, in-vehicle system 105uses in-vehicle database 432 during the guidance phase when thein-vehicle system detects that the vehicle is off route and it must plana new route.

[0149] For the destination entry phase, database 432 includes tablesthat are used by the in-vehicle system to determine the names of knowncities, the street names of streets in those cities (includingresidential, or side, streets), and the valid street address numbers onthose streets. The database also includes tables that specify types ofpoints of interest, and the points of interest of a particular type neara vehicle's location or in a particular city.

[0150] For the guidance phase, database 432 includes additional tablesthat the in-vehicle system uses to plan a route from a determinedlocation (latitude and longitude) to a desired destination or anintermediate point on a previously planned route. For instance, the mainroads network 1000 (FIG. 10) is stored in data tables in in-vehicledatabase 432.

[0151] Referring to FIG. 11, an AddressCityState table 1110 inin-vehicle database 432 includes a series of records that associate(Country,State,City) combinations with a series of (Street,AddressRange) combinations. A typical record 1112 in AddressCityState table1110 includes a Country field 1114 that references the name of a countryin a Country table 1120. Country table 1120 holds the textrepresentations of the names of known countries, such as “United States”or “Canada.” Record 1112 also has a CityState field 1116 which is areference to a CityState table 1130 that is used to determine the textrepresentation of a city and state in the country referenced by Countryfield 1114. Record 1112 also includes an AddressStreet field 1118 thatreferences the first of a range of records 1158 in an AddressStreettable 1150. Directly after record 1112 in AddressCityState table 1110, arecord 1113 includes an AddressStreet field 1119 that references thenext record 1153 after range 1158, thereby defining the records in range1158.

[0152] Each record in AddressStreet table 1150 is associated with acombination of a complete street name, and a range of valid streetnumbers for that street name. Multiple records in AddressStreet table1150 can refer to the same street name in order to build up an entirerange of valid street numbers. A typical record 1152 in AddressStreettable 1150 includes a Streetname field 1154 and an AddressRange field1156. Streetname field 1154 references a record in a StreetRecord table1160 that is used to form the text representation of the street name.AddressRange field 1156 references a record 1182 in AddressRange table1180 that includes entries for the lowest 1184 and highest 1186numerical values in a valid range of the street numbers for theassociate street.

[0153] StreetRecord table 1160 is used to form completely specifiedstreet names in terms of base street names, optional prefixes andsuffixes, and street types. For instance, “North Main Blvd” isrepresented by the base street name “Main,” the prefix/suffixcombination “North/-” and the street type “Blvd.” A typical record 1162in StreetRecord table 1160 includes a StreetName field 1164 thatreferences the text form of the base street name stored in a StreetNametable 1170, and an AffixType field 1166 that includes a representationof the prefix/suffix combination as an index to the predetermined set ofprefix/suffix combinations and a text representation of the street type.

[0154] Referring back to record 1112 in AddressCityState table 1110,CityState field 1116 references a record 1132 in CityState table 1130.Record 1132 includes a City field 1134 that encodes the textrepresentation of the name of the city, and a State field 1136 thatreferences a record 1142 in a State table 1140 that encodes the name ofthe state.

[0155] Several tables shown in FIG. 11 store lists of text names. Theseinclude Country table 1120, StreetName table 1170, State table 1140, andCityState table 1130. In FIG. 11, references to records are shown asproviding a direct access to the stored text representations. Referringto FIG. 12, a representative text table 1200 includes an index 1210 anda compressed text region 1220. A reference to a particular record isused as an offset to a record 1212 in index 1210. Record 1212 includes astarting field 1214 and a length field 1216. Compressed text 1220includes the concatenation of all the text records, encoded as asequence of 6-bit character representation. Starting field 1214 is theindex of the starting 6-bit character of the record. In order for aprocedure executing on onboard computer 210 to access the text string,the procedure first converts the index to the address of the starting8-bit byte of storage, and then it unpacks the 6-bit characterrepresentation to form a standard 8-bit character representation of therecord.

[0156] Referring to FIG. 14, an additional set of tables supports entryof a destination in terms of a “point of interest” (POI). Points ofinterest are divided by type, such as “restaurants,” “ATM machines,” and“gas stations.” A POIType table 1410 includes a sequence of records. Atypical record 1412 in POIType table 1410 includes a Type field 1414that references a record 1422 in a POITypes table 1420. Record 1422 is atext representation of the type of POI.

[0157] Record 1412 of POIType table 1410 includes an Offset field 1416that references a first record 1432 of a range 1444 of records in aPOINameCity table 1430. An Offset field 1417 of a record 1413 thatimmediately follows record 1412 in POIType table 1410 references arecord 1446 in POINameCity table 1430 that immediately follows range1444 of records in POIType table 1410.

[0158] Record 1432 in POINameCity table 1430 includes a Country field1434, which references a record in Country table 1120 (FIG. 11), aCityState field 1436, which references a record in CityState table 1130,a POIName filed 1438, and an Offset field 1440, which references arecord 1452 in a POIList table 1450 which is the first record in a range1464 of records in POIList table 1450 associated with record 1432. AnOffset field 1440 of a record 1433 that immediately follows record 1432in POINameCity table 1430 references a record 1466 that immediatelyfollows range 1464 in POIList table 1450.

[0159] Record 1452 in POILIst table 1450 includes a StreetName field1454, which references a record in StreetRecord table 1160, an Addressfield 1456 that encodes the street number associated with the address ofthe point of interest, a PhoneNumber field 1458 which encodes thetelephone number of the point of interest, and a Latitude/Longitudefield 1460 which encodes the latitude and longitude of the point ofinterest.

[0160] Additional tables are included in in-vehicle database 432 tosupport other forms of destination specification. In versions of thesystem that support destination specification in terms of a “YellowPages” (telephone directory) category, in-vehicle database 432 includesa text table of “Yellow Pages” categories. In versions of system thatsupport destination specification in terms of a pair of intersectingroads, a table of valid cross-street combinations is included inin-vehicle database 432. If a table of cross-street combinations isincluded, the table can alternatively include only intersections of mainstreets, or additionally include intersections of main streets andsmaller residential streets, or even intersections of pairs ofresidential streets, if sufficient storage is available in thein-vehicle system.

[0161] Additional tables in in-vehicle database 432 (FIG. 4) are usedduring the guidance phase when the vehicle is determined to be offroute. In particular, these tables encode main roads network 1000 (FIG.10). Referring to FIG. 13A, a representative link of main roads network1000 joins a node i 1301 and a node j 1302. Link c 1307 joins nodes i1301 and j 1302. Link c 1307 includes two shape points 1303 and 1303.Node i 1301 is also connected to links a 1305 and b 1306 and node j 1302is also connected to links d 1308 and e 1309.

[0162] Referring to FIG. 13B, several tables are used to represent themain roads network 1000. Records in these tables related to therepresentative link shown in FIG. 13A are illustrated in FIG. 13B. AMasterNode table 1310 includes one logically variable length record foreach node in the network. A record 1312 which is associated with node i1301 includes a Latitude/Longitude field 1314 that encodes the locationof node i 1301. Record 1312 also includes a set of link fields 1316, onefor each of the links joined at node i 1301. Each link field 1316includes information related to allowable turns from that link ontoother links at that node, and includes a reference to a record in aLinkSegments table 1330 associated with that link. For instance, thelink field 1316 associated with link c 1307 references record 1332 inLinkSegments table 1330.

[0163] Record 1332 in LinkSegments table 1330 includes a StreetNamefield 1334, which references a record in StreetRecord table 1160, and areference node field 1336 and a non-reference node field 1338 whichreference records 1312 and 1318 in MasterNode table 1310, respectively.Record 1332 also includes a ShapePointInfo field 1340 which references arecord 1352 in a LinkShapePoint table 1350. The record referenced byShapePointInfo field 1340 includes information related to the shapepoints on the link, as well as information related to signs on the link.Record 1332 also includes a Class field 1342, which encodes the roadclass of the link, and an AddressRanges field 1344, which references tworecords in AddressRange table 1180, one for each side of the road.

[0164] Record 1352 in LinkShapePoint table 1350 includes aNumberShapePoints field 1354 and a NumberSigns field 1356. For eachshape point, record 1352 includes an encoding of the change in latitudeand longitude from the previous shape point, or from the reference nodefor the first shape point. Record 1352 also includes SignInformation1360 describing the signs that would be seen by someone driving alongthe link.

[0165] 2.6 Server Software Components (FIG. 5)

[0166] Referring to FIG. 5, server system 125 includes software thatexecutes on server computer 310 (FIG. 3). This software includes anavigation application 512, which is used to interact with thein-vehicle systems. Navigation application 512 is coupled to acommunication interface 514, which is used to communicate with telephoneinterface 320 (FIG. 3). Navigation application is also coupled to a GPSinterface 516 that is coupled to GPS receiver 325 (FIG. 3).

[0167] Navigation application 512 also makes use of a number ofdatabases that it accesses through a data interface 518. Server system125 includes a server map database 520 that includes the complete roadnetwork 700 (FIG. 7). This database is derived from map information 360provided from map provider 160. The map information is processed by amap processor 550 that reformats the map information to form server mapdatabase 520. The same map information is used to derive the mapinformation that is stored in the in-vehicle databases 432 in thevehicles. Map processor 550 can be implemented as a software module thatexecutes on server computer 310, or can alternatively execute on someother computer allocated to the reformatting task. By deriving both theserver map database and the in-vehicle map database from the same mapinformation, consistency between the in-vehicle and the server data isguaranteed.

[0168] Navigation application 512 also makes use of a yellow pagesdatabase 522 that it uses to convert the telephone number of a desireddestination to a street address in a “reverse” number lookup. Theinformation needed to construct yellow pages database 522 is provided byan external information system 130, such as a telephone company or apublisher of telephone directories.

[0169] Navigation application 512 also makes use of a traffic database524. Information in traffic database 524 includes typical link speedsthat it uses for route planning. The information comes from acombination of an external information system 130, such as from agovernment run traffic monitoring authority, and from logging dataobtained from probe vehicles (see Section 3.5). If probe vehicles areused to collect traffic information, then traffic information can alsobe provided by the server system to the external traffic informationsystem.

[0170] 3 System Operation FIGS. 15A-B And 16-18

[0171] 3.1 General Procedure

[0172] System operation involves cooperation between in-vehicle system105 and server system 125 (see FIG. 1). The procedure followed from thetime at which an operator of a vehicle begins specifying a destinationto the time at which the vehicle reaches the specified destination isillustrated in the pseudocode listing in FIGS. 15A-B and 16-18.

[0173] Referring to FIG. 15A, the procedure followed by in-vehiclesystem 105 (FIGS. 1,2) from the time at which the operator beginsspecifying the desired destination to the time that the in-vehiclesystem can begin guiding the operator to the destination shown. Thein-vehicle system first accepts a destination specification from theoperator (line 1502). This can take several separate interactions withthe operator, for instance the operator selecting a city, then a street,and then a street number. Various types of destination specificationprocedures are supported by the system, as described further below (seeSection 3.2.1)

[0174] The in-vehicle system also determines the vehicle's initiallocation or data related to the vehicle's initial location, and in someversions of the system the orientation of the vehicle (line 1503). Thelocation or location-related data includes one or more of (a) a GPSlocation estimate or pseudorange measurements obtained at the time thatthe navigation request is being made, (b) past GPS-based locationestimates, and (c) dead-reckoning from previous GPS-based locationestimates or from maneuver locations. Starting location estimation isdiscussed further below (see Section 3.2.2)

[0175] After having accepted the destination specification from theoperator, and location data related to the vehicle's current location,the in-vehicle system establishes a communication session with theserver system (line 1504). The in-vehicle system establishes thecommunication session by making a cellular telephone call to the serversystem and then establishing a data communication session with theserver system using its modem.

[0176] The in-vehicle system then sends the location data and thedestination specification to the server system (line 1505).

[0177] Referring now to FIG. 15B, the server system accepts thecommunication session from the vehicle (line 1552) and receives thelocation data and the destination specification (line 1553).

[0178] The server system receives signals from multiple GPS satellites140 and computes GPS correction data for each of the satellites (line1554). The server system then determines the vehicle's location (line1555). In determining the vehicle's location, if the in-vehicle systemprovided raw GPS data, such as pseudorange measurements to GPSsatellites 140, the server system applies the GPS correction data it hascomputed to the raw GPS data that the vehicle provided to compute thevehicle's location.

[0179] In alternative versions of the server system, the server's GPSreceiver (or at least its GPS antenna) is not necessarily located at thecentralized server. For instance, the centralized server can be somedistance from the vehicles. The GPS receiver and antenna are locatednearer to the vehicles than the centralized server. This makes the GPScorrection data more accurate since the server system's GPS receiver isthen closer to the vehicles at which the GPS location estimates arebeing estimated. Also, a server system can have multiple GPS receiversin different locations. The server system then chooses the closest GPSreceiver to a vehicle for which it is providing correction data. In thisway, a single server system can service vehicles in a wide geographicarea over which common GPS correction data may not be effective duegeographic variations in the correction terms.

[0180] For certain types of received destination specifications, and inparticular, a destination specification in terms of a class of “yellowpages” categories, the destination is not fully specified at this point.If this is the case (line 1556) then further operator input may berequired in response to secondary specification data provided by theserver system. The server system sends the secondary data to the vehicle(line 1557). For instance, if the operator specified the destination interms of a yellow pages category, the server system provides secondarydata with the specific listings in that category that are near thevehicle's location.

[0181] Referring back to FIG. 15A, the in-vehicle system accepts thesecondary destination specification data (line 1507). Using this data,the in-vehicle system presents the data to the operator and accepts asecondary destination specification from the operator, for instance as achoice from the list of destinations defined in the secondaryspecification data. The secondary destination specification is sent tothe server (line 1509). At this point, the server system has acompletely specified destination.

[0182] Turning back to FIG. 15B, the server system now determines aroute (see Section 3.2.4) from the vehicle's location to the specifieddestination (line 1561). The server system also determines a spot maparound the vehicle's location that it will download to the vehicle (line1562). The server system also determines whether to download spot mapsaround maneuver points, for instance, based on the complexity of themaneuvers, and determines the spot maps around those maneuver points.

[0183] The server system sends the planned route, the spot map, and theGPS correction data to the in-vehicle system (line 1563).

[0184] Referring back to FIG. 15A, the in-vehicle system receives theplanned route, spot map, and GPS correction data from the server system(line 1512) and closes the communication session with the server (line1513).

[0185] Referring now to FIG. 16, the vehicle is now prepared to guidethe operator in a startup maneuver from its initial location onto theplanned route. First, the in-vehicle system initializes its estimatedlocation. The server system provided GPS correction data that thein-vehicle system provides to its GPS receiver in order to increase theaccuracy of the location estimates provided by its GPS receiver. The GPScorrection data that the server system provided is only valid for ashort time. After an interval of approximately one minute from the timethe GPS correction data was obtained by the server system from its GPSreceiver, the in-vehicle system stops using the correction data and usesstandard GPS instead. As is discussed further below, GPS correction datamay be obtained at other times during a trip, and in such cases, thein-vehicle system provides the correction data to its GPS receiver for afixed interval from the time that the data was generated by a GPSreceiver.

[0186] During the startup maneuver, which is the initial portion of thetrip until the vehicle is following the planed route, the in-vehiclesystem tracks the location of the vehicle using the differential GPSlocation estimates until the GPS correction data is too old, and thentracks the vehicle using uncorrected GPS location estimates (line 1604).The in-vehicle system displays the spot map along with an indication ofthe vehicle's estimated location and a representation of the plannedroute (line 1605). When the in-vehicle system detects that the vehicleis following the planned route, the startup maneuver phase is completedand a turn-by-turn route following phase begins.

[0187] Referring now to FIG. 17, the route following procedure is basedon notifying the operator of each of the links along a planned route.While traveling along the route, the in-vehicle system maintains twolocation estimates for the vehicle. The first is based on GPS estimates,or on DGPS estimates if current GPS correction data is available. Thesecond location estimate is based on a “dead reckoning” procedure. Thisprocedure assumes that the vehicle is properly following the plannedroute. The dead reckoning uses the locations of the maneuver and waypoints along the planned route and information from the vehicle sensors,in particular, from the velocity sensor, to update this second locationestimate. If the vehicle is truly following the route, then the twolocation estimates should remain close to one another. Note that thisdead reckoning procedure does not need to use heading estimates to trackthe vehicle's position since the vehicle is assumed to be travelingalong the planned route.

[0188] Along each link, after the initial maneuver at the starting nodeof the link, the in-vehicle system initializes an off-route tolerance.This tolerance is the allowable disparity between the GPS and the deadreckoning location estimates. The tolerance grows from an initial valueestablished right after a maneuver to account for a growing inaccuracyin the estimates, due, for instance, to calibration inaccuracies in thevelocity sensor and aging of the GPS correction data. The off-routetolerance is initialized to 150 feet and grows linearly to a maximum of500 feet at a rate of about 1 foot per 100 feet traveled.

[0189] While traveling to the next maneuver point (loop starting at line1704), the vehicle increases the off route tolerance (line 1705), tracksits dead reckoning position (line 1706), and tracks its GPS or DGPSposition (line 1707) (depending of whether current GPS correction datais available).

[0190] If at any time the difference between the dead reckoning positionand the (D)GPS based position is more than the off-route tolerance, thena off-route routine is initiated (line 1710).

[0191] While traveling along a link, the vehicle eventually reaches apoint near the next maneuver. When the vehicle is estimated to be withina distance window of the next maneuver, then the operator is notified bythe in-vehicle system using graphical and aural output of the upcomingmaneuver. The size of the notification window depends on the road classbeing traveled on, which is related to the time prior to a maneuver thatan operator is notified of the maneuver. For instance, on a highway, anoperator is notified of a maneuver, such as exit from the highway, at afarther distance from the maneuver that the distance than from amaneuver in a residential neighborhood.

[0192] Also while traveling along the link, the in-vehicle systemattempts to detect the precise point at which the next maneuver iscarried out. When the vehicle is within a distance window of the nextmaneuver, the in-vehicle system attempts to detect the maneuver. Forinstance, if the maneuver involves making a right angle turn, thesignals from the in-vehicle sensors, such as from a magnetic compass ora rate gyroscope, or from successive GPS location estimates from whichchanges in directions are detected, provide a clear indication of themaneuver point.

[0193] If a maneuver is detected (line 1718) then the in-vehicle systemupdates its dead reckoning location estimate based on the location ofthe maneuver (line 1719). Also, the in-vehicle system uses thedownloaded location of the maneuver point to compute its own GPScorrection data (line 1720). In particular, the in-vehicle systemcomputes the deviation in latitude and longitude at the maneuver pointand applies these deviations as corrections to the latitude andlongitude position estimates output from its GPS receiver for a oneminute interval after the maneuver. Alternatively, the in-vehicle systemuses the location of the maneuver point and the pseudorange measurementsobtained by the vehicle's GPS receiver at the time of the detectedmaneuver to compute new GPS correction data that are used for a oneminute interval after the maneuver.

[0194] Note that there are times when a maneuver is not detected, forinstance if it involves only a slight turn that is not accuratelydetected using the vehicle sensors. In such a case, the in-vehiclesystem continues the dead reckoning procedure under the assumption thatthe vehicle has stayed on route. Such maneuver points that are notdetected are essentially treated in the same way as way points from thepoint of view of tracking the dead reckoning location of the vehicle.

[0195] The route following procedure continues from link to link alongthe route until the destination is reached (line 1725).

[0196] Referring now to FIG. 18, the off-route routine first involves adead-reckoning position correction procedure (lines 1802-1810). If forthe direction of travel matches the planned route for an interval, forinstance, of 75 feet after the difference between the position estimateswas detected, then the dead reckoning position is updated to be theclosest point along the planned route to the (D)GPS position estimate(lines 1804-1805). In this way, if the deviation in position estimatesis due to inaccurate tracking of the distance along the route, thelocation correction procedure should successfully overcome the error. Ifthe deviation between the (D)GPS estimate and the dead-reckoningestimate is now less than the off-route tolerance, the in-vehicle systemresumes the route following procedure (line 1808). If on the other hand,even the closest point on the planned route is still more than theoff-route tolerance from the (D)GPS position, then the locationcorrection procedure is not successful and a route replanning procedureis initiated.

[0197] Referring still to FIG. 18, the route replanning procedureinvolves first estimating the vehicle's location on main roads network1000 (FIG. 10) that is stored in the vehicle. The GPS location estimateis used to find a link along which the vehicle is traveling (line 1811).

[0198] Once the vehicle has been located on the main roads network, thein-vehicle system calculates a best route that leads to one of themaneuver or way points along the previously planned route (line 1813).

[0199] The newly planned route to the maneuver or way point on theprevious route, along with the remaining portion of the previouslyplanned route then becomes the new planned route which replaces theprevious one (line 1815). The link-by-link route following procedure isthen reentered (line 1816).

[0200] Specific aspects of the general operation of the system aredescribed in the following sections. These aspects includes routeplanning, including in-vehicle destination specification as well ascomputation of the best route at the server system. The specific aspectsalso include the guidance operations carried out by the in vehiclesystem, as well as route replanning operations carried out by thein-vehicle system when it detects that the vehicle is off route. Inaddition, operation of the system in which the fleet of vehicles is usedto collect traffic related data is described below.

[0201] 3.2 Route Planning (FIGS. 15A-B)

[0202] Route planning involves several steps, as shown in FIGS. 15A-B.In particular, the route planning operation includes:

[0203] Destination specification (line 1502, FIG. 15A)

[0204] Starting location determination (line 1503, FIG. 15A)

[0205] Querying the server system (lines 1504-1510, FIG. 15A; lines1552-1560, FIG. 15B)

[0206] Route planning (line 1561, FIG. 15B)

[0207] Route and spot map downloading (lines 1562-1563,

[0208]FIG. 15B, line 1512, FIG. 15A) Specific operations carried out bythe in-vehicle and server systems in each of these steps are describedin the following sections.

[0209] 3.2.1 Destination Input

[0210] As shown in FIG. 15A (line 1502), the first phase of navigationto a desired destination is destination input by the operator of thevehicle. In-vehicle system 105 (FIGS. 1,2) enables the operator tospecify a destination in a number of different ways. In general, thein-vehicle system uses in-vehicle database 432 (FIG. 4) to providealternative in scrolling lists from which the operator chooses. Adestination specification can be one of:

[0211] A street address (e.g., city, street, and number),

[0212] A point of interest (e.g., city, type of point of interest, and aselection from a list),

[0213] A “yellow pages” listing (e.g., type of listing, and a selectionfrom a list),

[0214] A telephone number of the destination,

[0215] A pair of cross streets,

[0216] A selection from a list of recently specified destinations, and

[0217] A selection from a list of previously stored destinations in auser's “profile”.

[0218] In an initial interaction with the system, the operator firstspecifies what method of destination input will be used, for example, byselecting from a displayed list of choices.

[0219] 3.2.1.1 Street Address Specification

[0220] One way that the operator can specify a destination is by thestreet address of the destination. The destination specification in thiscase is a fully specified (country, state, city, street, number)combination. The user does not necessarily have to enter each of thesefields in turn. For instance, the current (i.e., previously used)country and state can be used as defaults.

[0221] Alternative sequences of field specifications can be used. In onesequence, the operator first selects a city from a scrolling list ofcities in the current (country, state). Referring to FIG. 11, the listof valid states is obtained from CityState table 1130. After theoperator selects a desired city, the in-vehicle system presents ascrolling list of valid streets names in that city. The list of validstreet names is obtained using AddressCityState table 1100, andassociated AddressStreet table 1150, StreetRecord table 1160, andStreetName table 1170. After the operator selects a desired street, theoperator enters a street number. The in-vehicle system validates thenumber using AddressStreet table 1150 and AddressRange table 1180.

[0222] In the above procedure, alternative methods of selecting fromlists of valid names can be used, including scrolling through a listusing “up” and “down” buttons, and spelling a prefix of the name untilit unambiguously specifies a full name. An alphanumeric keyboard is notnecessarily provided with this system. If one is not provided, theoperator enters letters of a spelling, or digits of a street address, bymoving a cursor to a display of the desired letter or digit andselecting that letter or digit.

[0223] There are times when the city of the desired destination is notknown. In that case, the city can be initially left unknown. The list ofvalid street names presented to the operator by the in-vehicle system isthen all the streets in the current state. After the street name isselected, if the city is ambiguous, the operator selects from the listof possible cities and then proceeds to input the street number.Alternatively, disambiguation of the city of a destination street can beleft until after a street number is also specified.

[0224] 3.2.1.2 Point of Interest Specification

[0225] In specifying a destination by a point of interest (POI), theoperator first selects from a list of types of points of interests.Examples of types of POIs include banking locations, gas stations,hospitals, and restaurants. Referring to FIG. 14, the list of validtypes is obtained by the in-vehicle system from POITypes table 1420.

[0226] The operator can select a particular POI of the selected POI typein a number of ways. In a first way, the operator next selects a city inwhich to find the destination POI. Using POINameCity table 1430, thesystem displays a list of names, addresses and phone numbers of POIs ofthe selected type in the selected city. The operator then selects fromthe list of displayed POIs. The phone number can be useful, forinstance, if the operator wants to call the destination, such as arestaurant, before deciding to travel to the destination.

[0227] Rather than specifying the city, the system can display the POIsby their proximity to the current location of the vehicle. The GPS-basedlatitude and longitude estimates are compared to the Latitude/Longitudefield of records in POIList table 1450, for POIs of the selected POItype. The in-vehicle system then displays the POIs in order of proximityto the current location rather than alphabetically.

[0228] 3.2.1.3 “Yellow Pages”

[0229] In order to support an operator specifying a destination to thein-vehicle system using “yellow pages” listings, the in-vehicle database432 does not have the capacity to include all the possible listings thatan operator may be looking for. Instead, only the categories of listingsare included, for example, “jewelry stores.” The in-vehicle system firstdisplays a list of categories from which the operator selects aparticular category. The operator then selects a particular destinationcity, or requests listings in the proximity of the current location. Thein-vehicle system presents a list of categories to the operator and theoperator selects from the list. Note that the destination is notcompletely specified at this point since a particular destination (i.e.,a street address) has not yet been determined.

[0230] After the communication session with the server is established,the server downloads the specific listings in the selected yellow pagescategory to the in-vehicle system, either according to the selectedcity, or according to the proximity to the vehicle's location. Theoperator then selects from the downloaded list.

[0231] 3.2.1.4 Other Destination Specifications

[0232] Several optional ways of specifying a destination can also besupported by in the in-vehicle system.

[0233] An operator can specify a destination by selecting a pair ofcross streets. To support selection of a pair of cross streets,in-vehicle database 432 includes a table of valid pairs of main streets,and possible pairs of main and side streets or even pairs of sidestreets. The operator selects a first street. A list of valid crossstreets are then displayed and the operator selects one from the list.

[0234] As in destination specification by street number, if the city isnot specified before specifying the cross streets, the city isdisambiguated after one or both of the street names are selected.

[0235] An operator can specify a destination by specifying the telephonenumber of the destination. A complete telephone directory is not storedin in-vehicle database 432, therefore, the validity of the telephonenumber, other than perhaps the validity of the area code, is notverified before the in-vehicle system establishes the communicationsession with the server system. The server system receives the telephonenumber and looks in up in a “reverse” telephone directory to determinethe street address of the destination.

[0236] As is described further below, individual operators can havestored profiles that are stored in the vehicle and may havecorresponding storage on the server system. This profile can holdtypical destinations, such as “work,” “home,” “airport,” etc. for whichthe operator has previously specified particular locations.

[0237] An operator can specify a destination by selecting from the mostrecently specified locations. For example, the operator may be returningto a recently visited work site.

[0238] Alternative versions of the system allow specification of adestination by street address, but the in-vehicle system does not havedata with which to validate the address ranges for the specified street.For instance, the in-vehicle system may not have the capability tovalidate any street numbers, or the destination may be outside ageographic range for which it has stored address range data. If thein-vehicle system cannot validate the street address, it neverthelessestablishes a communication session with the server computer. The servercomputer then completes the validation procedure.

[0239] 3.2.2 Starting Location Determination

[0240] The in-vehicle system sends to the server system either anestimate of its position, or sends raw GPS data from its GPS receiverfrom which the server system computes the vehicle's position (line 1503,FIG. 15A).

[0241] There are situations in which the vehicle cannot receive signalsfrom the GPS satellites at its starting location. For example, thiswould be the case if the vehicle were in an underground garage. In sucha case, the vehicle relies on location estimates that the system madeprior to reaching the starting location. Furthermore, after a GPSreceiver is first powered on, there can be a significant interval beforewhich it can provide location estimates. For example, the GPS receivermust locate each of the satellites that are in range, and compute theirlocations in orbit.

[0242] The in-vehicle system therefore maintains a history of GPSlocation estimates on an ongoing basis, even when the operator is notbeing guided along a route. This history is stored in a non-volatilememory in the in-vehicle system before the system is shut off.Therefore, if GPS signals cannot be received at the starting location,the latest GPS location estimate in the stored history is used.

[0243] In addition to sending location related data to the serversystem, the in-vehicle system also sends speed and orientation data. Theorientation can be obtained from either past consecutive GPS locationestimates, or from the magnetic compass. The speed and orientationinformation is used by the server system, for example, to disambiguatewhich of a number of nearby road segments the vehicle is on based on theclass of road segments and the allowable directions of travel on thosesegments.

[0244] If the vehicle was guided to the starting location during aprevious navigation session, the starting location can be based on deadreckoning along the previously planned route.

[0245] Once the server system provides GPS correction data to thein-vehicle system, the in-vehicle system updates its starting locationusing the GPS correction data (line 1602, FIG. 16). For instance, if theGPS correction data is pseudorange correction data, the in-vehiclesystem provides the pseudorange correction data to its GPS receiver andreceives the corrected position estimate from the GPS receiver. If theGPS correction data is offsets in latitude and longitude, the in-vehiclesystem applies these offsets to the estimated position output from itsGPS receiver.

[0246] 3.2.3 Server Query

[0247] When the in-vehicle system establishes a communication sessionwith the server system (line 1504-1510, FIG. 15A), it does so in twosteps. First the in-vehicle system establishes a cellular telephoneconnection to the server system, and then it establishes a modulateddata session on the cellular telephone connection.

[0248] In the first step, the cellular telephone connection isestablished by the in-vehicle system dialing a specific number to reachthe server system. The in-vehicle system can handle typical errorconditions that might be found in an analog cellular telephone network,such as being out of range of the cellular system, or the cellularsystem not having the capacity to establish the call.

[0249] In the second step, once the telephone connection is set up, thein-vehicle system attempts to establish a data connection with theserver system. Typical modems carry out a negotiation phase in whichcompatible modulation, compression, and error correcting protocols areselected. In order to reduce the time needed to set up the communicationsession, a particular set of protocols is preselected, for example asthe “lowest” common protocol that all vehicles support. The serversystem expects communication using this lowest protocol. This allowsdata to flow as soon as possible without waiting for the protocolnegotiation phase to be completed. Since the amount of data to betransferred is relatively small, the time taken in negotiating the bestprotocols would likely be larger than the time saved by sending the datausing the negotiated protocol rather than with the preselected protocol.

[0250] 3.2.4 Route Planning

[0251] Route planning at the server system (line 1561, FIG. 15B) useswell known route finding approaches. In particular, two instances of thewell-known A (“A-Star”) graph search algorithm are used in conjunctionwith road network 700 (FIG. 700). One instance of the A algorithm startsat the starting location and one starts “backwards” from the desireddestination. The A algorithm is a type of “best first” search approach.At any point executing the algorithm, the actual distance along thegraph from an initial node to a set of intermediate nodes has beencomputed. A lower bound (or in some versions of the algorithm, anestimate) of the distance from each of the intermediate nodes to thefinal node is added to the actual distance. The intermediate node withthe lowest sum is extended. If the lower bounds are used, this algorithmproduces the shortest path from the initial node to the final node.Using the two instances of the A* algorithm, a best path is chosen afterthere are intermediate nodes in common for the two instances of thealgorithm.

[0252] Alternatives to the A* route planning algorithms can be used. Forinstance, Dijstra's algorithm, or another type of best first algorithmcan be used.

[0253] Route planning can be based on a variety of criteria. A shortesttotal distance uses the actual link distances in the road network todetermine the cost of a path. The lower bound on the remaining path canbe straight-line distance between an intermediate node and the finalnode. Route planning can alternatively be based on lowest expectedtravel time. Travel time along a link can be based on an expected speedfor different road classes, or can be based on specific speed datastored on the server system and associated with particular links. Forexample, the server system may know that certain links are congestedwith slower than expected speeds for their road classes. The routeplanning algorithm would then tend to avoid such a congested link ifthere are alternative routes that can be taken.

[0254] Other alternative route planning approaches can also be used onthe server system. For instance, routes can be constrained to followparticular road segments, and the cost of routes can include otherfactors than distance or expected travel time, such as toll fees alongthe route.

[0255] 3.2.5 Route and Spot Map Download

[0256] Referring to FIGS. 8 and 9, the server system downloads a routeas a sequence of links joined by maneuver points, and downloads spotmaps as small graphs around the starting location or the selectedmaneuver points (lines 1562-1563, FIG. 15B, line 1512, FIG. 15A). Inorder to reduce the download time needed, this data is represented as acompact data structure.

[0257] The planned route is downloaded as a sequence of route linksusing a compressed format. For each link in the planned route, thedownloaded information includes:

[0258] The latitude and longitude of the starting node (maneuver point)of the link, encoded as 32-bit integers in units of 10⁻⁵ degrees,

[0259] Turn information, encoded as an index representing messages suchas “turn right,” “keep left,” etc.,

[0260] The number of “arms” at the current maneuver point,

[0261] The number of way points before the next maneuver, and

[0262] The rank (e.g., the size or classification) of the road segmentassociated with this link.

[0263] In addition, for each way point, the data for a link includes:

[0264] The change in latitude and longitude from the previous way point,or from the starting node for the first way point, encoded as 12-bitintegers in units of 10⁻⁵ degrees.

[0265] Note that 12-bit encoding of the change in latitude or longitudelimits the change to approximately 2¹²×10⁻⁵=0.04 degrees. If a segmentof the route planned by the server system includes a greater changebetween successive maneuver or way points, the server system insertsadditional way points that are sufficiently close to encode the changesin the 12-bit quantities.

[0266] In addition, for each link, the downloaded data includes:

[0267] The length of text fields, if any, associated with the name ofthe street associated with the link, and the name of the street to beturned onto at the next maneuver point, and with any signage or otherspecial information to be presented to the operator, and

[0268] The text fields themselves.

[0269] For each “arm” at a maneuver point, the downloaded data includesdata related to the angles at which the intersecting streets join at themaneuver point, thereby allowing a relatively accurate graphicalrepresentation of the maneuver to be displayed to the operator.

[0270] This route download format provides a compact representation thatcan be downloaded quickly from the server to the vehicle. Alternativeversions of the system can take advantage of data in the in-vehicledatabase to reduce the amount of data still further, for example, byreferencing stored street names or by using references to nodes in themain roads network that is already stored in the vehicle. Alternativeversions of the system can also include additional information relatedto the links. For example, link travel speeds can be downloaded,particularly if the links are known by the server to be exceptionallycongested.

[0271] An alternative approach to route downloading includes use ofpredefined sequences of road segments that are stored in the in-vehiclesystems. The server system replaces an sequence of road segments,maneuver points, and waypoints, with a reference to the stored predefinesequence. In this way, typically traveled routes, for example, along ahighway do not have to be downloaded explicitly. The server system canperiodically update the stored sequences in the vehicles to reflect thetypically requested routes by those vehicles. Alternatively, thein-vehicle system retains a memory of previously downloaded routes, andthe server can refer to portions of those routes when downloading anewly planned route.

[0272] 3.3 Guidance

[0273] Guiding the operator to the desired destination involves severalaspects of operation of the in-vehicle system. These include:

[0274] A startup maneuver (FIG. 16),

[0275] Dead reckoning location tracking (FIG. 17, line 1706),

[0276] GPS location tracking and off-route detection (FIG. 17, lines1707-1710), and

[0277] Maneuver notification and detection (FIG. 17, lines 1712-1722).

[0278] These aspects are described in the following sections.

[0279] 3.3.1 Startup Maneuvers

[0280] There are several reasons that an operator may not be able tofollow an initial route. One is inaccuracy of the initial location of avehicle. For instance, the GPS may indicate that the vehicle is on astreet, when in fact it is in a nearby parking lot or an adjacentstreet. Also, if a vehicle is pointing in the opposite direction on astreet than the server system expects, then the vehicle is likely to gooff route right from the very first step. Also, following directions atthe start of a route can be difficult, for instance, due to the closespacing of side streets, inadequate signs, distractions, traffic, etc.

[0281] For these and other reasons, the system does not rely on anoperator making no mistakes right from the very initial startinglocation. Instead, the starting location is used to determine the spotmap that is downloaded to the vehicle. The spot map typically coversonly two or three intersections in any direction from the startinglocation. The planned route is shown in conjunction with the spot map,as is the vehicle's DGPS based location. The operator uses this maprepresentation to get onto the planned route.

[0282] Once the vehicle is on a segment of the planned route, andtraveling in the correct direction, the turn-by-turn guidance phasebegins.

[0283] 3.3.2 Dead Reckoning Location Tracking

[0284] Once the in-vehicle system enters the turn-by-turn routefollowing (guidance) phase, the in-vehicle system maintains a deadreckoning location estimate of the vehicle. In general, the in-vehiclesystem tracks the vehicle under the assumption that the operator istrying to follow the instructions. Dead reckoning is based on convertingthe velocity signal from velocity sensor 232 and the straight lineapproximations of the links between maneuver or way points along theplanned route into an updated location. In particular, if the in-vehiclesystem assumes that the vehicle is at a known maneuver point, then asthe vehicle travels a distance measured according to the velocitysignal, the in-vehicle system estimates the vehicle's location as thepoint that is the measured distance along the sequence of links from themaneuver point. The locations of the nodes at the ends of each link areknown to the in-vehicle system, therefore, the in-vehicle systemessentially uses the direction of the links to estimate the directionthat the vehicle is traveling as it leaves the maneuver point, and as itpasses over subsequent links on the route.

[0285] Dead reckoning relies on a known correspondence between thevelocity signal and the distance traveled. Several factors affect thiscorrespondence, including tire pressure which is affected bytemperature, which affects the circumference of the tires. In order toimprove the accuracy by which the distance traveled is estimated fromthe velocity signal, an ongoing calibration procedure is supported. Whenthe in-vehicle system detects a maneuver, it compares the velocitysensor-based distance estimate and the map-based distance estimate. Thein-vehicle system adjusts a scale factor relating the number of velocitysignal pulses to the distance traveled so that the velocity sensor andmap-based traveled distance estimates match.

[0286] 3.3.3 GPS Location Tracking and Off-Route Detection

[0287] While the operator is being directed from maneuver to maneuveralong the planned route, the in-vehicle system continuously updates itsGPS-based location estimate while the GPS satellite signals arereceived. In addition, there are intervals during which the in-vehiclesystem has current GPS correction data that it provides to the GPSreceiver in order to improve the accuracy of the GPS-location estimates,for instance, in a differential correction mode.

[0288] GPS correction data is received by the in-vehicle system from theserver system when the planned route is downloaded. In alternativeversions of the system, there may be other times at which the serverprovides differential correction data, for instance during communicationsessions that are established for another purpose.

[0289] The in-vehicle system can also compute its own GPS correctiondata when it knows its location precisely. The in-vehicle systemestimates its location very accurately when it detects that a plannedmaneuver is executed by the operator, since an accurate location of eachmaneuver is downloaded for the server system when the planned route isdownloaded.

[0290] Therefore, while negotiating the planned route, the in-vehiclesystem receives a stream of GPS or DGPS based location estimates. Theselocation estimates are compared on an ongoing basis to the deadreckoning position estimates also maintained by the in-vehicle system.

[0291] After a vehicle executes a maneuver, and in particular when GPScorrection data is computed based on the location of the maneuver pointand the raw GPS data recorded when the vehicle passes through themaneuver point, the GPS-based location and the dead-reckoning positionsshould match. As a vehicle correctly passes along the planned link, thedead-reckoning position and the GPS-based position are expected todiverge somewhat for several reasons. These reasons include increasederror in the GPS estimates, and possible map errors.

[0292] The GPS correction data is provided to the GPS receiver forapproximately one minute after the maneuver. During that time, theirutility slowly decreases, that is, the error of the DGPS based locationestimates slowly increases. After the GPS correction data is no longerused, the GPS error is expected to remain within a fixed range.

[0293] The error in the dead reckoning position estimate grows primarilydue to error in estimating the distance traveled along the links. Alsomap errors, both in the length of links and the location of waypoints ormaneuver points, can contribute to a growing dead reckoning positionerror.

[0294] The combination of a growing error in each of the two terms iscompensated for by using an increasing tolerance beyond which anoff-route condition is detected by the in-vehicle system. The tolerancestarts at 150 feet. The tolerance increases at a rate of 1 foot per 100feet traveled until the tolerance reaches 500 feet.

[0295] If at any point the difference between the two location estimatesexceeds the tolerance, the in-vehicle system detects an off-routecondition it attempts to correct the dead reckoning position estimateand it that is unsuccessful, it executes a route replanning procedure(see Section 3.4).

[0296] 3.3.4 Maneuver Notification and Detection

[0297] Maneuver notification and detection both use the dead reckoningposition estimate, or more particularly, use a dead reckoning estimateof the scalar distance traveled along the planned route from apreviously detected maneuver.

[0298] The in-vehicle system gives instructions to the operator atdistance prior to when the in-vehicle system expects the vehicle toexecute the next maneuver. This accounts for both the reaction timeneeded by the operator, as well as inaccuracy in the system's estimateof the distance to the next maneuver. In order to account for thedifferent amount of time or distance needed by an operator to act on acommand, the instructions are given farther from the next maneuver onhigh-speed links, such as highways, than on small residential streets.Each road class has a fixed distance from an upcoming maneuver at whichthe next instructions are given.

[0299] The in-vehicle system also gives voice prompts as the vehicleenters the notification window. Graphical and text prompts andinstructions are displayed at least from the point that the vehicleenters the notification window, and can be displayed sooner.

[0300] In a distance-based window around the point at which thein-vehicle system expected the next maneuver to be carried out, thein-vehicle system attempts to detect the exact point at which themaneuver occurs. For instance, if the maneuver involves a right angleturn, the output of the onboard magnetic compass or the GPS-baseddirection estimate is used to reliably detect the maneuver. Also,sensing of the vehicle speed to detect certain classes of maneuvers,such as stopping at a toll booth.

[0301] Certain maneuvers cannot be detected with high accuracy. Forinstance, a turn may be too gradual to detect using the signal producedby a magnetic compass. If the vehicle leaves the maneuver detectionwindow without detecting the expected maneuver, then the in-vehiclesystem simply continues to update the dead reckoning position until asubsequent maneuver is detected.

[0302] 3.3.4.1 Display and Voice Commands

[0303] In addition to receiving audible instructions, the maneuvernotification and instructions are provided on the in-vehicle display.The display include:

[0304] A graphical illustration of the “distance to go” until the nextmaneuver, or example as a bar chart that gradually fills as the link istraversed,

[0305] A digital “distance to go,” for instance a number in miles orfeet,

[0306] A graphical representation of the upcoming road geometry at thenext maneuver, for instance showing the angles at which all roadsmeeting at the next intersection joint, and

[0307] Sign text that should be visible at the next maneuver point.

[0308] Voice instructions include a variety of pre-stored phrases,including commands to notify a driver of an upcoming maneuver, andcommands to instruct and operator to make a maneuver at the point thatthe instruction is give.

[0309] 3.4 Route Replanning

[0310] When the in-vehicle system detects that a vehicle is off theplanned route, it executes a route replanning procedure (FIG. 18). Thefirst step is to determine where the vehicle is traveling on the mainroad network 1000, which is stored in in-vehicle database 432.

[0311] The in-vehicle system uses the GPS (or DGPS) based latitude andlongitude estimates to search through the list of nodes in MasterNodetable 1310. Sequential GPS-based position estimates, or the output ofthe magnetic compass, are used to determine a direction of travel alonga link joining to adjacent nodes. This then determines which link inLinkSegments table 1330 the vehicle is traveling on, and the directionof travel along that link.

[0312] The in-vehicle system then executes a shortest path search (e.g.,an A* search) starting at that link to one of the maneuver or way pointsalong the planned route. A number of points, or alternatively allpoints, on either side of the last maneuver point are used as points atwhich the replanned route can join up with the previously planned route.For instance, ten points before and after the last detected maneuverpoint can be used. Limiting the number of points can reduce the amountof computation (time and memory) required to replan the route. If thereare fewer than ten remaining points, then the actual desired destinationis one of the points that the replanned route can “join” to plannedroute.

[0313] As in the server system based route planning approach, thein-vehicle system uses an A* algorithm to plan the route. The startingpoint is determined using the scanning of MasterNode table 1310, asdescribed above. As intermediate nodes are considered in the A* search,the lower bound on the distance to the desired location is minimum overthe maneuver and way points near the last detected maneuver point of thesum of the straight-line distance from the intermediate point to themaneuver or way point plus the previously calculated distance along thepreviously planned route from that maneuver or way point to the desireddestination. In this way, the best point of rejoining the previouslyplanned route is found.

[0314] As in the server system based route planning, the cost oftraveling over a link can be based on the length of the link, anestimate of the time to travel over the link based on the road class ofthe line, or an estimate of the time to travel a link based on specificroad speed information associated with that link.

[0315] 3.5 Floating Vehicle Data Collection

[0316] Referring to FIG. 19, navigation application 512 which is part ofserver system 125 makes use of a traffic database 524 when planningroutes that are based on expected travel time. In the description of thesystem above, traffic information provided from an external informationsystem 130, such as from a government run traffic monitoring authority,is used to populate traffic database 524.

[0317] In addition to relying on an externally provided trafficinformation, server system 125 makes use of some or all vehicles 100 as“probes” for collecting traffic information. Navigation application 512receives the traffic information from the probe vehicles and feeds thecollected traffic information back into traffic database 524 Inaddition, the server system optionally sends updated traffic informationto the external information system. In this way, the vehicle navigationsystem can be a source of traffic information in addition to, or insteadof, being a consumer of traffic information from external informationsystem 130.

[0318] Two modes of data collection are used. First, ongoing traffic“profile” data is collected by the in-vehicle systems in probe vehicles.Occasionally, the probe vehicles upload their collected data to theserver system and the server system updates its traffic database basedon the uploaded information. In the second mode, the in-vehicle systemsin the probe vehicles detect when the vehicle's speed is significantlyslower than would be expected based on the class of road being traveled,on or based on traffic related data that is stored in the vehicle andwhich relates the expected speed to the road segment being traveled on.When the in-vehicle system detects that the vehicle's speed is slowerthat expected, that is, it detects any exception from expected trafficconditions, it immediately reports the exception to the server system sothat the server system can update its traffic database 524 to reflectsunexpected traffic conditions.

[0319] 3.5.1 Traffic Profile Collection

[0320] In the first mode of traffic data collection, navigationapplication 412 in in-vehicle system 105 of a probe vehicle collects onan ongoing basis a history (a profile) of the speed that the vehicletravels on links of the main roads network (or equivalently the transittimes on the links). The in-vehicle system collects the traffic profiledata independently of the guidance function. That is, the vehicle doesnot have to be guided by the navigation system in order to collecttraffic profile data. The navigation application stores the time of dayand the speed traveled on each link in a link speed log 1920.

[0321] In order to build up link speed log 1920, the in-vehicle systemtracks the vehicle's location on main roads network 1000 that is storedin in-vehicle database 432. Using the GPS location estimates it receivesfrom its GPS receiver, the in-vehicle system detects when the vehicle isfollowing a road segment (link) of the main roads network. Thein-vehicle system records the time the vehicle takes to travel from oneend to the other of the link and stores a reference to the link, thetime of day, and the speed traveled along the link in the link speedlog. As the vehicle travels over multiple links of the main roadsnetwork, a series of travel times is logged, each associated with a linkthat was traversed.

[0322] Occasionally, for example when vehicle leaves the main roadsnetwork, or periodically, such as daily, the in-vehicle system sends thelogged profile information it has stored in link speed log 1920 to theserver system over a data connection that the in-vehicle systeminitiates over a cellular telephone connection with the server system.After it has sent the information, the in-vehicle system clears its linkspeed log.

[0323] The operator of the vehicle has the option of enabling ordisabling either mode of data collection through the user interface ofthe in-vehicle system. Also, the server system can enable (or request)either type of collection. For instance, the server system can enablemore vehicles if it needs more data, and disable data collection in somevehicles if it is receiving more data than it needs.

[0324] At the server system, navigation application 512 receives thelogged speed information from a number of probe vehicles. Using thiscollected information, the navigation application updates trafficdatabase 524. For example, the navigation application incorporates thereported speeds for a particular link into an average speed for thatlink that is stored in its traffic database. Optionally, the serversystem provides the updated traffic information to external informationsystem 130.

[0325] On the server system, traffic database 524 includes an averagelink speed for each link (in each direction), as well as a start and astop time for a morning and an evening rush “hour” (busy period). Foreach busy period, the traffic database includes the average speed duringthat period.

[0326] Various alternative intervals can be used. For instance, equalfive-minute intervals can be used, as can unequal intervals, such as 1hour intervals in the middle of the night and five-minute intervals attypically busy periods.

[0327] Optionally, the average link speeds stored in the server system'straffic database 524 are downloaded and stored in a link speeds database1910 in the in-vehicle system of each vehicle. This link speeds databaseis used, for instance, by the in-vehicle system when replanning a routebases on a shortest expected travel time.

[0328] 3.5.2 Exception Reporting

[0329] In the second mode of traffic data collection, the in-vehiclesystem makes use of information in its link speeds database 1910, whichincludes expected travel speeds for all the links in main roads network100. Multiple travel times are stored for each link, for instance, toaccount for the variations due to morning and evening busy periods. Foreach link, the following information is recorded:

[0330] Typical expected speed

[0331] Start and end times of the morning busy period

[0332] Expected speed during the morning busy period

[0333] Start and end times of the evening busy period

[0334] Expected speed during the evening busy period

[0335] Alternatively, other types of intervals can be used to store thespeed information. Also, rather than relying on specific speedinformation for a link, the in-vehicle system can alternatively base thetypical expected speed for a link on the class of the link. Forinstance, a link on a class 4 (highway) link can be typically expectedto be close to the speed limit (e.g., 55 MPH).

[0336] As in the profile data collection mode, the in-vehicle system ofa probe vehicle tracks the location of the vehicle using GPS locationestimates as it traverses links of the main roads network, and detectswhen the vehicle traverses particular links in the main roads network.The in-vehicle system detects that a traffic exception has occurred if atravel speed along a link is substantially slower or faster thanexpected (e.g. 75% of the expected speed or slower) for that link atthat time of day.

[0337] When a traffic exception occurs, the in-vehicle systemestablishes a communication session with the server system by placing acellular telephone call to the server system. The in-vehicle systemtransmits a short data message encoding the exception, identifying thelink and the travel speed, to the server system.

[0338] In an alternative approach to exception reporting, a vehiclemakes a probabilistic choice of whether to transmit the exceptionmessage. In this alternative, not all vehicles which encounter theexception transmit to the server system, thereby reducing thecommunication load on the server system.

[0339] The server system receives the exception message from thein-vehicle system. The server system updates traffic database 524, whichit uses to plan routes, based on the exception messages it receives fromthe probe vehicles. If there is a sufficient “density” of probe vehicleson the road network, the server system will typically receive exceptionmessages from multiple probe vehicle. Therefore, optionally, the serversystem can require that two or more probe vehicles report an exception(i.e., a traffic exception is confirmed by another vehicle) beforeupdating its traffic database.

[0340] The server system resets its expected speeds for the links onwhich exceptions have been reported after a period of time when no moreexceptions are reported by probe vehicles for those links.

[0341] Operation of the exception data collection mode does notnecessarily require intervention of the operator. The operator of aprobe vehicle can explicitly enable or disable exception reporting.Also, the in-vehicle system can be configured so that the operator isasked to confirm the validity of exception information before it is sentto the server system. For instance the in-vehicle system can display theexception message to the operator and the operator must press a buttonindicating that the message is valid before it is sent to the serversystem. This confirmation approach avoids having a vehicle report anexception when slow speed is due to a non-traffic related reason, suchas stopping for gas along the link.

[0342] In a alternative version of the system, exceptions are loggedrather than immediately reported to the server system. The in-vehiclesystem then uploads the logged exceptions to the server system in thesame way that it can upload logged profile data.

[0343] 3.6 Server Control

[0344] In an alternative version of the system, the system controls thevehicle data collection, for instance, to limit the rate at which itreceives data from probe vehicles, or to receive data related toparticular regions or roadways. Alternative methods of controlling thecollection include the following.

[0345] In a first alternative, the probe vehicles do not transmit theirlogged speed data unless queried by the server system. The server systempolls (interrogates) vehicles to receive their logged speed data. In oneapproach, the server system polls vehicles based on the geographicregion in which the vehicles typically travel. For instance, if theserver system does not have up-to-date data for roads in a region, itpolls vehicles that typically travel in that region. To poll a vehicle,the server system places a cellular telephone call, or otherwisenotifies the vehicle, the in-vehicle system. The in-vehicle systemreceives the call and provides its logged speed data to the server. Forexample, an alternative to placing a telephone call is to broadcast amessage to a number of vehicles over a broadcast channel, such as on asideband of a commercial radio broadcast. In another approach to thisalternative, the server system polls vehicles for which it has recentlyprovided planned routes and which it expects will have logged speed datafor road segments on those routes.

[0346] In another alternative, the in-vehicle systems place the calls tothe server system to transfer logged speed data, but the server systemhas previously provided instructions to the in-vehicle system regardingwhen to initiate that call. For instance, when the server systemprovides a planned route to the in-vehicle system, the planned route isaccompanied by an instruction to call the server system after thevehicle has passed a particular road segment.

[0347] In another alternative, whenever an in-vehicle system calls theserver system, the server system optionally requests the vehicle'slogged speed data. In the case that the vehicle is calling for a routeplanning service, the data transfer occurs during the interval betweenthe upload of the desired destination and the start of the download ofthe planned route, or in any other interval that would have otherwisebeen unused for data transfer from the vehicle to the server system.

[0348] In another alternative, when the server system provides a plannedroute to an in-vehicle system, the planned route includes the serversystem's up-to-date expected link times (i.e., the link times reflectrecently received probe data). In this alternative, traffic exceptionson a segment are not reported to the server if the server system wasalready aware of the exception at the time that it planned the route.

[0349] 3.7 Data Fusion

[0350] In alternative versions of the system, the server system receivestraffic related information from external information services. Forinstance, the server system receives traffic incident reports (e.g.,breakdown reports) that it uses to predict slow travel speeds, ratherthan waiting to receive data from probe vehicles for those segments.Similarly, the server system receives information related to events(e.g., sporting events) that it uses to predict link speeds. The serversystem combines these predicted link speeds with link speeds reported byprobe vehicles when calculating new routes for in-vehicle systemsaccording to as shortest expected travel time criterion.

[0351] 4 Vehicle Updating (FIGS. 20A-C)

[0352] In the system described above, in-vehicle system and the serversystem include data that is kept consistent. For instance, the mainroads network stored in the in-vehicle system includes a subset of theroads network on the server system. When the data is consistent, adestination specification that is validated by the in-vehicle systemwill be valid for the server system as well.

[0353] The information used by the overall navigation system is updatedfrom time to time. For example, the map provider may provide periodicupdates to the road network to correct previous errors or to reflectchanges in the road network, such as addition of a new road.

[0354] Alternative versions of the system use one or more approaches toupdating the in-vehicle system to keep the in-vehicle and systemdatabases consistent. When the databases are consistent a destinationspecification that is validated by an in-vehicle system will not befound to be invalid by the server system when it tries to plan a routeto the destination. Conversely, when the databases are consistent, thein-vehicle will not rule out a destination specification that the serversystem would have found to be valid, for example because a new road hasbeen added to the road network.

[0355] The system also includes the provision to update the software inaddition to the data for the in-vehicle system. For instance, the userinterface for existing functionality can be changed by downloading newcode. Also, entirely new functionality can be downloaded. This new orchanged functionality can include modified menus and graphics that areused to interface with the operator.

[0356] New software and interface definitions are integrated into thein-vehicle system using one of several well-known alternativetechniques. For example, new software modules can provide predefinedentry points that are accessed from existing software modules in thein-vehicle system. Data describing the interfaces to new softwaremodules can be downloaded with the code that implements the modules.User interface definitions can be implemented using low-level code thatmanipulates the pixels on the display, or can use a high-leveldescription such as one using a markup language (e.g., HDML).

[0357] The navigation system uses one or more of the followingalternative approaches to updating the in-vehicle system:

[0358] Physically replacing a static storage device in the in-vehiclesystem,

[0359] Updating over a high-speed data link, for example at a dealershipor other service center, and

[0360] Updating over a cellular telephone based data link.

[0361] Each of these approaches are described in the following sections.

[0362] 4.1 Physical Replacement of the Storage Device

[0363] Referring to FIG. 20A, in a first approach, static storage 222 inonboard computer 210 in in-vehicle system 105 is a removable device. Forinstance, static storage 222 can be a PCMCIA card housing a magneticdisk or a flash memory system.

[0364] Updating the in-vehicle system involves replacing storage device222 with another storage device 222 a that has been preloaded with anupdated version of the databases. This enables the entire database to beupdated quickly, for instance, when the main roads network needs to beupdated to correspond to a different geographic area.

[0365] 4.2 Updating over a High Speed Data Link

[0366] Referring to FIG. 22B, a second approach to updating thein-vehicle system involves transferring data to the in-vehicle systemover a high-speed (e.g., up to 1 Mb/s) data connection. The in-vehiclesystem includes a data interface 2020 that is connected to onboardcomputer 210 in in-vehicle system 105. A source of the update data isconnected to the data interface. For instance, a high-speed connection2010 can be connected to service equipment 2030 at a dealership or aservice center which downloads the updated information using industrystandard communication protocols, such as Ford's SCP or the SAE J1850protocol. Alternatively, an owner of a vehicle can connect a personalcomputer 2031 (such as a laptop computer) to the in-vehicle system.Updates for the in-vehicle system would be obtained by the owner on arecorded medium 2040, such as a CD-ROM, or over the Internet. Connection2011 between the personal computer and the in-vehicle system can use awireless connection, such as an infra-red link.

[0367] Referring to FIG. 20C, another alternative approach to updatingthe in-vehicle system is to use a wired telephone connection. In thisapproach, the in-vehicle system includes a moderate speed modem 2050(e.g., a 56 kb/s modem) and a telephone connector. The owner provides aphysical connection 2052 from the telephone connector to the publictelephone network (PSTN) 340. The in-vehicle system places a telephonecall to the server system, or another server used to provide dataupdates, and downloads the data at a moderate speed over the telephoneconnection.

[0368] 4.3 Updating over a Wireless Link

[0369] A third approach to updating the in-vehicle database uses awireless data connections between the in-vehicle system and the serversystem, such as over a cellular telephone connection. The amount of datathat can be transmitted in a reasonable time (e.g., less than an hour)is limited by the relatively slow data transfer speeds that can beachieved over such connections. Typically, the database is incrementallyupdated over a wireless data connection rather than an entire new copyof the database being downloaded.

[0370] One of several alternative approaches to initiating a databaseupdate over a wireless data connection with the server system are used.First, an operator can explicitly request an update through the userinterface of the in-vehicle system. Second, an update can be requestedby an in-vehicle system based on an elapsed time since a prior update.Third, database edits can be downloaded prior to or after downloading aplanned route after the in-vehicle system establishes a communicationsession with the server system. Fourth, the server system can placetelephone calls to each of the vehicles and “push” the edit updates toeach vehicle in turn.

[0371] In order to maintain consistency between the in-vehicle data andthe server system's data, data in the database is associated with aversion number. Each time the server system updates its data, it updatesthe version number. When a vehicle requests a route, it also providesthe version number of the data that was used to validate the destinationspecification of the route. The server system uses the received versionnumber to identify which, if any, updates have not yet been downloadedto the calling vehicle.

[0372] The server does not necessarily have to download all updates inone session. Instead, it provides updates incrementally. In theincremental approach, the most relevant updates are provided first. Forinstance, the server system updates the main roads network in the cityin which the vehicle typically travels prior to downloading updates foranother city.

[0373] If an in-vehicle system has an out-of-date database, thevalidated destination specification that it sends the server system maybe invalid due to changes in the road network. For instance, a streetname may have changed. Therefore, if the server system receives aninvalid destination specification from the in-vehicle system, the serversystem notifies the in-vehicle system which notifies the operator. Theoperator can then specify another address, or wait for updatedinformation to be downloaded to the vehicle from the server system.

[0374] 5 Additional Services

[0375] In addition to providing navigation services, alternativeversions of the vehicle information system provide additional servicessuch as roadside assistance, remote vehicle control, trafficinformation, and communication related services.

[0376] 5.1 Emergency and Roadside Assistance

[0377] Emergency and roadside assistance provides an operator of avehicle with a way of contacting assistance and providing the locationof the vehicle. Referring to FIG. 21A, in an operator initiatedinteraction, the operator selects the emergency and roadside assistanceoption on the user interface of the in-vehicle system. The vehicleplaces a cellular telephone call to the server system, or to anotherserver that the in-vehicle system has been configured to call to handlesuch requests. When the call is established, the in-vehicle systemestablishes a data connection to the called server. The in-vehiclesystem transfers a unique identification of the vehicle to the server.The unique identification is used by the server to access informationsuch as the make, model, and color of the vehicle, which may be usefulto a dispatched service vehicle finding the operator's vehicle. Thein-vehicle system also sends its estimated location, or raw GPS data,and most recent direction of travel based on its GPS measurements. Theserver system applies GPS correction data to the vehicle's estimatedlocation or raw GPS data to determine a corrected location estimate.After the in-vehicle system transfers the data to the server, theoperator can communicate with a telephone operator 2110 at the serverusing the telephone handset in the vehicle. This allows the operator toprovide details that may be useful in dispatching assistance.

[0378] In addition to operator-initiated requests for assistance, thein-vehicle system includes a mode in which activation of the air-bagsystem, or some other indication of an emergency situation,automatically initiates a request for assistance. This mode would beused, for example, if the vehicle is involved in a collision and theoperator is unable to or does not think to call for assistance.

[0379] 5.2 Remote Vehicle Control

[0380] Another additional service is remote vehicle control. Thein-vehicle system is coupled to vehicle subsystems, such as the doorlocking subsystem, or the vehicle control subsystem. This coupling canuse standard vehicle data communication infrastructure found in manyvehicles today, such as the SCP (the Standard Corporate Protocol) busfound in vehicles manufactured by the Ford Motor Company.

[0381] 5.2.1 Door Unlocking

[0382] Referring to FIG. 21B, remote door unlocking is an example of aremote vehicle control service. When an operator is locked out of his orher car, he or she contacts the server system, for example, by placing atelephone call to a telephone operator with access to the server system.After appropriate authentication by the telephone operator, thetelephone operator initiates a remote door unlocking procedure that isexecuted by the server system.

[0383] The vehicle's cellular telephone receiver is not typically lefton when the operator has left the vehicle in order to reduce batteryusage. Therefore, the server system does not, in general, simply make atelephone call to the in-vehicle system to unlock the doors.

[0384] On a precise schedule, the in-vehicle system repeatedly powers upthe cellular telephone receiver to determine whether an incoming call isbeing placed at that time. For instance, the in-vehicle system repeatsthis cycle every 15 minutes. If the in-vehicle system does not detect acall, it powers down the telephone receiver until the next scheduledlistening time.

[0385] The vehicle's schedule is stored at the server system, and thein-vehicle system and the server system share a common time base, forexample based on GPS signals. The server system waits until the lockedvehicle's next scheduled listening time to make a cellular telephonecall to establish a data communication channel with the in-vehiclesystem. Once a data connection is established, the server system sends acommand to the in-vehicle system to unlock the doors.

[0386] When the operator of the vehicle requests the door unlockingservice from the telephone operator, the telephone operator informs thevehicle operator of the time that the doors will be unlocked, since theschedule of vehicle listening times is available to the telephoneoperator.

[0387] 5.2.2 Vehicle Immobilization

[0388] A vehicle immobilization service uses a similar strategy as thedoor unlocking service. A vehicle operator calls a telephone operator atthe centralized server to notify the telephone operator that the vehiclehas been stolen. The server system can either make a telephone call tothe in-vehicle system immediately, if the telephone receiver in thevehicle is powered on, or relies on the scheduled power-up mode that isused for the door unlocking functionality described above.

[0389] In either case, when the in-vehicle system and the server systemcommunicate, the in-vehicle system provides the vehicle's location tothe server system, and the server system provides to the in-vehiclesystem a command to disable the vehicle. The in-vehicle system thensends a command to a vehicle system to disable the vehicle.

[0390] 5.3 Traffic Information

[0391] The traffic information service provides an operator with areport of traffic conditions on a small set of previously specified“trips.” For instance, an operator may have a choice of threealternative ways of getting go from home to work. When the operator isabout to begin the trip, he or she interacts with the in-vehicle systemto request traffic information on those trips. The in-vehicle systemcontacts the server system, which provides current traffic informationfor the operator's trips.

[0392] One approach by which the operator specifies his or her “trips”uses an onboard stored table of a set of trip segments. These segmentswould typically involve many segments of the road network. For instance,a portion of a major highway between two intersecting highways might betrip segment. The operator “builds” the personal trips by choosing asubset of trip segments. When the in-vehicle system contacts the serversystem to determine traffic conditions on the operator's personal trips,the in-vehicle system transfers the operator's selected trip segments tothe server system.

[0393] The server system uses its traffic database, which includecurrent link speeds on segments of the road network, to determine thecurrent traffic conditions on the operator's trips. Various alternativepresentations of the traffic conditions can be used. In this version ofthe system, the traffic conditions are categorized into a small numberof categories, such as normal, congested, and severely congested, andeach category is displayed graphically to the operator using a differenticon.

[0394] In alternative versions of the system, the server system activelycontacts a user if an exceptional traffic condition occurs on one of theuser's previously specified trips. For instance, the server system cansend the information to the in-vehicle system by calling the in-vehiclesystem, or send a pager message, send email, or place a telephone callto the user informing the user of the exceptional condition.

[0395] In another alternative, the user specifies several alternativetrips. When the server system detects an exceptional traffic conditionon one of the user's specified trips, it actively downloads trafficinformation related to the alternative trips. In this way, the user doesnot have to wait for the in-vehicle system to make a call to the serversystem to replan the route.

[0396] 6 Extensible Server Architecture (FIG. 22)

[0397] Referring to FIG. 22, an alternative server system 125 a providesthe functionality of the server system 125 described above, and inaddition provides an extensible architecture for providing otherservices to the vehicles. Server system 125 a includes multiple servercomputers coupled over a LAN 2205. Alternatively, the functionality ofthese server computers can be implemented on a smaller number ofcomputers, or on a single computer that implements all their functions.

[0398] Server system 125 a includes a gateway system 2210 that iscoupled to telephone interface 320. Gateway system 2210 is used toprovide a communication gateway between vehicles 100 and servercomputers in server system 125 a, and implements a message routingfunction so that communication received from an in-vehicle system isdirected to the appropriate server computer. Gateway system 2210 doesnot necessarily have to interpret the content of data passing betweenthe server systems and the vehicles.

[0399] The server computers include a navigation system 2250 on whichthe navigation application described above executes. When an in-vehiclesystem initiates a communication session with server system 125 a torequest a route planning service, gateway system 2210 determines thatthe session should be connected to navigation system 2250 usinginformation provided by the in-vehicle system in the communicationsession. For instance, the in-vehicle system identifies the navigationservice in the initial portion of the data stream. Alternatively,different services implemented by server system 125 a have differenttelephone numbers that are assigned to telephone interface 320, andgateway system 2210 routes the communication to the appropriate servercomputer based on the number called by the in-vehicle system.

[0400] Navigation system 2250 implements the functionality of serversystem 125 as shown in FIG. 5. That is, it includes an interface to GPSreceiver 325, and includes server map database 520, yellow pagesdatabase 522, and traffic database 524. Navigation system 2250 iscoupled to map provider 2252, and a traffic information system 2254.

[0401] Another service provided by server system 125 a is implemented bya communication system 2260. Communication system 2260 is coupled toexternal communication systems, including an email system 2262 and apaging system 2264. These external communication systems forwardmessages addressed to particular vehicles to communication system 2260.Communication system 2260 requests from gateway system 2210 that a datacommunication channel be established with the particular vehicles, andthen passes data and commands to the in-vehicle systems.

[0402] The in-vehicle systems in the vehicles include software modulesthat correspond to the services provided by the server system. Forinstance, communication sent from communication system 2260 to anin-vehicle system is received by a communication module that interpretsthe data and commands it receives. For instance, a message communicationmodule displays paging or email messages on the display of thein-vehicle system, or alternatively plays them as synthesized speechmessages.

[0403] A news system 2270 provides a service which sends data tovehicles which corresponds to news stories that are of interest to aparticular vehicle operators. The news stories are provided by anexternal news service 2272.

[0404] Server system 125 a also includes a remote configuration system2230 that is coupled to LAN 2205, and that is also coupled to theInternet. Using the remote configuration system, users of the navigationsystem can modify their records in user profiles 2232 that are stored atthe server system. A user's profile is downloaded by the server systemto the in-vehicle system in that user's vehicle, or can alternatively bestored on the server system. Information in the user profiles caninclude various types of information, including stored destinations thatthe user can select from when specifying a destination to the in-vehiclesystem. For instance, a user can specify a list of frequent destinationsover the Internet, and then later in the vehicle choose a particulardestination in that list by selecting from a display of the list by thein-vehicle system.

[0405] Another aspect of the user's profile relates to the trafficinformation service. Rather than having to define a set of trips usingthe in-vehicle interface, the user selects trips using a graphicalmap-based interface. For instance, an entire map of the highway systemor the main roads network is displayed. The user selects paths on thegraph by selecting sequences of trip segments. These trips aredownloaded to the user's vehicle, or can be stored by the server system.If they are stored at the server system, when the user initiates atraffic information request in the vehicle, the in-vehicle system doesnot necessarily transfer the specifications of the operator's trips,rather it specifies the identity of the operator and the server systemlooks up the operator's stored trips.

[0406] A user's profile can also include preferences such as particularroads the user wants to avoid. The user's profile can alternativelyinclude a time saving above which the user is willing to use a road thathe or she otherwise wants to avoid.

[0407] A user also uses remote configuration system 2230 to input routeplanning requests. For instance, the user provides a destinationspecification to the remote configuration system and the server systemdownloads a planned route to the destination prior to the user enteringthe vehicle. The user can access the remote configuration system in avariety of ways, including over the Internet, and over a voice telephoneconnection interacting with an automatic speech recognition device atthe server. In addition to specifying a destination, the user can alsorequest notification of when he or she needs to start the trip in orderto get to the destination at a particular time. The notification can beby telephone, pager, or using any of a variety of other notificationmethods.

[0408] A new service is added to server system 125 a by adding a servercomputer, updating gateway system 2210 so that communication for thatservice is routed to the new server computer, and updating thein-vehicle system by adding a corresponding software module to each ofthe in-vehicle systems. The in-vehicle systems are updated either over acellular telephone connection, or over a physical connection, asdescribed above (see Section 4).

[0409] Alternative version of the system do not necessarily include allthe features described above. For instance, a traffic information systemcan include operator specified trips. The in-vehicle system contacts aserver system for traffic information for those trips. The in-vehiclesystem does not need a GPS receiver, or a map database, of otherfeatures to support this feature alone.

[0410] In another alternative, the in-vehicle system does notnecessarily support autonomous route replanning. The in-vehicle systemcan contact the server to replan the route, or to provide a map which ituses to replan the route, when the in-vehicle system detects that thevehicle has gone off-route.

[0411] An alternative version of the system provides a “detour”capability. In particular, an operator indicates a road segment thatshould be removed from a planned route, and the in-vehicle system plansa detour around that road segment using its main roads database.

[0412] In another alternative version of the system, the server systemplans and downloads several routes, for instance planned according todifferent criteria, such as shortest time, shortest distance, etc. Thein-vehicle system displays characteristics of the alternatives (e.g.,time, distance) and the operator selects one. If the server have not yetdownloaded al the routes, only the selected route is continued to bedownloaded.

[0413] In another alternative version of the system, additional data isdownloaded from the server system along with the route. For instancetraffic information is downloaded and displayed to the operator. Also,advertising information, for example, for restaurants along the routeare downloaded and displayed to the operator and the vehicle passesalong the route.

[0414] In another alternative, traffic information is downloaded to thevehicle, for instance, according to a set of trips that have beenspecified by the operator. The traffic information is displayed alongwith a map of the road network. Traffic information is indicated usingone of a variety of techniques, including text annotations, icons, orusing color.

[0415] In another alternative, the server system does not download spotmaps to the in-vehicle system. The in-vehicle system providesturn-by-turn instructions from the starting locations. For instance, thefirst instruction may be “proceed to street X,” accompanied by an arrowindicating the direction the street X.

[0416] In another alternative, the in-vehicle system has a main roadsnetwork for autonomous replanning, but does not include address-rangedata for validating street addresses. The in-vehicle system insteadrelies on the server system to validate the street number specified byan operator. In this way, the in-vehicle system validates and addresspartially and relies on the server system completing the validation.

[0417] The same server system can concurrently support in-vehiclesystems with different capabilities, such as the alternativecapabilities described above.

[0418] Another alternative version enables an operator to specify asequence of destinations. For example, the first destination can be agas station, and the second destination is the operator's work. All thedestinations in the sequence are validated before the in-vehicle systemcontacts the server system. The server system plans a route from thestarting location to the first destination, and then from onedestination to the next. The server system downloads the entire plannedroute to the in-vehicle system.

[0419] It is to be understood that the foregoing description is intendedto illustrate and not to limit the scope of the invention, which isdefined by the scope of the appended claims. Other embodiments arewithin the scope of the following claims.

What is claimed is:
 1. A method for guiding a vehicle through a roadnetwork from a starting location to a destination, the methodcomprising: transmitting a specification of the destination to a server;and receiving from the server a specification of a planned route throughthe road network to the destination.
 2. The method of claim 1 furthercomprising receiving from the server a map that includes a specificationof the road network in the vicinity of the planned route.
 3. The methodof claim 1 wherein the specified part of the road network is in thevicinity of the starting location.
 4. The method of claim 1 wherein thespecification of the planned route includes specifications of aplurality of maneuvers to be carried out by the vehicle, and wherein thespecification of each maneuver includes a location of the maneuver. 5.The method of claim 1 wherein the specified part of the road network isin the vicinity of one or more maneuver locations.
 6. The method ofclaim 1 further comprising displaying the received map in conjunctionwith a representation of the planned route, and a location of thevehicle.
 7. The method of claim 6 further comprising estimating thelocation of the vehicle, and detecting when the vehicle is following theplanned route.
 8. A method for guiding a vehicle comprising:transmitting a specification of a location to a server; and receivingfrom the server a map that includes a specification of the a network inthe vicinity of the specified location.
 9. Software recorded on acomputer readable medium for causing an in-vehicle computer to performthe functions of: sending a specification of a destination to a server;accepting from the server a specification of a planned route through aroad network to the destination; and accepting from the server a mapthat includes a specification of the road network in the vicinity of theplanned route.
 10. A method for providing navigation information to avehicle comprising: receiving from a vehicle a specification of adestination; determining a planned route on a road network to thedestination; transmitting to the vehicle a specification of the plannedroute; and transmitting to the vehicle a map that includes aspecification of the road network in the vicinity of the planned route.11. A method for tracking a vehicle comprising: receiving a referencesignal from a positioning system; computing position data related to thelocation of the vehicle using the received reference signal;transmitting the position data to a server; receiving from the serverposition correction data; determining estimated coordinates of thevehicle including combining data computed from the received referencesignal and the position correction data.
 12. The method of claim 11wherein computing the position data, and determining the estimatedcoordinates, including combining the position data and the positioncorrection data, are performed repeatedly for an interval of time usingthe same received position correction data, and the method furthercomprises, subsequent to the interval of time, repeatedly computing theposition data and determining estimated coordinates of the vehicle usingthe position data without using the correction data.
 13. The method ofclaim 12 wherein: receiving the reference signal from a positioningsystem includes receiving signals from a plurality of positioningsatellites; computing the position data includes computing a rangemeasurement to each of the positioning satellite; receiving the positioncorrection data includes receiving range correction data for rangemeasurements to the positioning satellites; and combining the positiondata and the position correction data includes combining the rangemeasurements and the range correction data.
 14. The method of claim 12wherein: receiving the position correction data includes receiving alocation correction; and combining the position data and the positioncorrection data includes computing uncorrected coordinates from theposition data and adding the location correction to the uncorrectedcoordinates to determine the estimated location of the vehicle. 15.Software recorded on a computer readable medium for causing anin-vehicle computer to perform the functions of: receiving a referencesignal from a positioning system; computing position data related to thelocation of the vehicle using the received reference signal;transmitting the position data to a server; receiving from the serverposition correction data; determining estimated coordinates of thevehicle including combining data computed from the received referencesignal and the position correction data.
 16. An in-vehicle navigationsystem comprising: a positioning system receiver for receiving referencesignals from a positioning system; a wireless communication interfacefor accepting data signals from a server; and a processor coupled to thepositioning system and to the wireless communication system, wherein theonboard computer is programmed to perform the functions of acceptingreference data from the positioning system receiver, determiningposition data from the reference data, providing the position data tothe wireless communication interface for transmission to the server,accepting position correct data from the communication interface, anddetermining estimated coordinates for the vehicle from the referencedata and the accepted position correction data.
 17. The system of claim16 wherein the processor is further programmed to perform the functionof timing an interval during which it determines the estimatedcoordinates for the vehicle from the reference data and the acceptedposition correction data, and after which it determines the estimatedcoordinates for the vehicle from the reference data and without usingthe accepted position correction data
 18. A method for tracking avehicle comprising: receiving a specification of a first location, thespecification including coordinates of the first location; determiningwhen the vehicle is at the first location; computing first position datausing a reference signal received from a positioning system at the timeat which the vehicle was determined to be at the first location;computing position correction data using the first position data and thecoordinates of the first location; computing second position data usinga reference signal received from the positioning system at a second timesubsequent to the time at which that the vehicle was determined to be atthe first location; determining coordinates of the vehicle at the secondtime including combining the correction data and the second positiondata.
 19. The method of claim 18 wherein the specification of the firstlocation includes a specification of a maneuver to be carried out by thevehicle at the first location, and determining when the vehicle is atthe first location includes detecting when the vehicle performs thespecified maneuver.
 20. Software recorded on a computer readable mediumfor causing an in-vehicle computer to perform the functions of:receiving a specification of a first location, the specificationincluding coordinates of the first location; determining when a vehicleis at the first location; computing first position data using areference signal received from a positioning system at the time at whichthe vehicle was determined to be at the first location; computingposition correction data using the first position data and thecoordinates of the first location; computing second position data usinga reference signal received from a positioning system at a second timesubsequent to the time at which that the vehicle was determined to be atthe first location; determining coordinates of the vehicle at the secondtime including combining the correction data and the second positiondata.
 21. A vehicle navigation system comprising: a positioning systemreceiver for receiving reference signals from a positioning system; afirst storage for holding a specification of a first location, thespecification including coordinate of the first location; a secondstorage for holding position correction data; a vehicle sensor forsensing motion of the vehicle; and a processor coupled to thepositioning system receiver, to the first and the second storage, and tothe vehicle sensor, and programmed to perform the functions ofdetermining when the vehicle is at the first location using signals fromthe vehicle sensor, accepting first reference data related to thelocation of the vehicle at the time at which the vehicle was determinedto be at the first location from the positioning system receiver,computing position correction data using the first reference data andthe coordinates of the first location, and determining coordinates ofthe vehicle at a second time subsequent to the time at which that thevehicle was determined to be at the first location using the computedposition correction data.
 22. A method for detecting when a vehicledeviates from a planned route comprising: tracking a first estimatedposition of the vehicle using signals from a positioning system that arereceived at the vehicle; tracking a second estimated position of thevehicle using an estimate of the distance traveled along the plannedroute; detecting that the vehicle has deviated from the planned routewhen the first estimated position and the second estimated positiondiffer by at least a tolerance distance.
 23. The method of claim 22wherein the planned route includes a first point and a path followingthe first point, and wherein tracking the second estimated positionincludes detecting when the vehicle is at the first point on the plannedroute and estimating the distance traveled along the path following thefirst point.
 24. The method of claim 23 further comprising adjusting thetolerance distance, including reducing the tolerance distance when thevehicle is detected to be at the first point on the planned route, andincreasing the tolerance distance as the vehicle travels along the pathfollowing the first point.
 25. Software recorded on a computer readablemedium for causing an in-vehicle computer to perform the functions of:tracking a first estimated position of a vehicle using signals from apositioning system that are received at the vehicle; tracking a secondestimated position of the vehicle using an estimate of the distancetraveled along the planned route; detecting that the vehicle hasdeviated from the planned route when the first estimated position andthe second estimated position differ by at least a tolerance distance.26. A vehicle tracking system comprising: a first position estimatorincluding a positioning system receiver, for determining a firstestimate of the vehicle's location determined using information receivedfrom the positioning system receiver; storage for a planned route; asecond position estimator coupled to a vehicle motion sensor and to thestorage for the planned route, for determining a second estimate of thevehicle's location using information received from the vehicle sensorand the planned route; and an off-route detector coupled to the firstposition estimator and to the second position estimator, for comparingthe first estimate of the vehicle's position and the second estimate ofthe vehicle's position.